Economic sanctions,military interventions,and civil conflict outcomes

Abstract

Sanctions are designed to reduce the amount of resources available to the targeted actor and have the potential to be an effective tool for bringing disputing sides in a civil conflict to the bargaining table by altering incentives for continued fighting. Thus, there is reason to believe that sanctions can shorten the duration of civil conflicts. However, once sides in a conflict have moved to the use of violence to settle their dispute, it is hard for sanctions, in isolation, to impose enough cost to convince warring factions that settling a conflict has greater value than what could be expected from continued fighting. In this article, we argue that sanctions, in isolation, are unlikely to affect the duration of civil conflicts. However, when sanctions are combined with military interventions they can contribute to conflict management strategies resulting in shorter civil conflicts. We test our expectations empirically using data on civil conflicts from the Uppsala Conflict Data Program Armed Conflict Database and data on economic sanctions from the Threat and Imposition of Economic Sanctions Database. Our results suggest that the best hope for sanctions to shorten the duration of civil conflicts is if they are used as part of a comprehensive international response that includes institutional sanctions and military interventions.

Keywords

civil conflicts interventions sanctions

Introduction

The study of the effectiveness of sanctions to achieve foreign policy goals has generated a significant debate over if or when they ‘work’.¹ Likewise, the study of interventions into civil wars has provided significant insights into when or how outside actors can influence internal conflicts. There have, however, been a relatively limited number of studies investigating the role of economic sanctions in civil conflicts. In this article we examine how economic sanctions in conjunction with military interventions influence the duration of civil conflicts.

The paucity of systematic research on sanctions and civil conflicts holds despite the historical precedence for the use of sanctions to influence the outcomes of domestic struggles. Hufbauer et al. (2007), for example, identify ten separate cases where the explicit goal of the sanctioning state(s) was to bring an end to a civil war, six cases where the goal was to ease state repression, and another 22 cases where a goal of the sending nations was to weaken or destabilize an existing government. Using the latest version of the Threat and Imposition of Economic Sanctions dataset (Morgan, Bapat & Kobayashi, 2014) and civil conflict data from the Uppsala Conflict Data Program (UCDP) Armed Conflict Dataset, v.4 (Themnér & Wallensteen, 2015), we find that nearly half of the civil conflict country-years between 1950 and 2005 have sanctions imposed on the government.²

A recent example of the use of economic sanctions as a tool of foreign policy in civil conflicts can be found in the Syrian civil war that began in 2011. While the United States had been sanctioning Syria since 2004 in an attempt to manipulate their political behavior, the USA and others imposed tough new sanctions on the Syrian government in an effort to pressure the warring parties to enter peace negotiations. At the same time, external actors were supplying the Syrian rebels with resources to keep them viable as a challenge to the Syrian regime. On the face of it, sanctions do not appear terribly effective at bringing the warring parties to the negotiating table. However, an implied objective of the United States in both the imposition of sanctions and the support of the Syrian rebels is to generate a settlement that brings the conflict to an end. Thus, governments still believe that sanctions can be a viable tool for managing civil conflicts and this seems to hold as the USA and its allies and Russia have engaged in a prolonged campaign of air strikes within Syria. The objective today (late 2015) seems to be a renewed diplomatic effort.

Our goal in this article is to examine the theoretical and empirical linkages between the use of economic sanctions, military interventions, and the ending of civil conflicts. After developing our theoretical argument and empirical tests we draw inferences that should inform the policy and scholarly communities on the efficacy of sanctions in the context of civil conflict. For example, one implication of our results is that neither sanctions nor military interventions, in isolation, are likely to significantly shorten civil conflicts. However, when institutions impose sanctions and military interventions accompany the sanctions, the durations of civil conflicts are significantly shortened.

Economic and military interventions into civil conflicts

In one of the earlier quantitative studies of the role of sanctions in the resolution of civil conflicts, Strandow (2006) focused on arms sales and commodity transfers during UN sponsored targeted sanctions and threats of sanctions. Using a bargaining model, he demonstrated that sanctions can change actors’ beliefs about the distribution of power and in doing so influence the movement toward conflict resolution by generating convergence on the ‘true’ capabilities between actors. However, this holds only when sanctions are imposed in a consistent and unequivocal manner. This bargaining lens forms the foundation for much of the research into the influence of interventions on the outcome of civil wars as well, and Strandow’s (2006) results support the findings of several earlier studies showing that military or economic interventions can prolong conflict (Regan, 2000; Balch-Lyndsay & Enterline, 2000; Elbadawi & Sambanis, 2000; Collier, Hoeffler & Söderbom, 2004; Regan & Aydin, 2006).

Escribà-Folch (2010), also using a bargaining framework, found that international sanctions are negatively associated with civil war length, which runs counter to many earlier studies on the role of external interventions (e.g. Regan, 1996). Escribà-Folch’s (2010) research demonstrates that when international institutions were involved in sanctions, the likelihood that a civil war ended through a negotiated settlement significantly increased. In contrast, unilaterally imposed sanctions were found to be significantly linked with military victory. Escribà-Folch (2010) argued that sanctions can shorten the duration of civil wars by revealing information that brings expectations of victory into convergence with ‘true’ probabilities of victory.

Brzoska (2008) investigated the impact of military sanctions on mediation in civil war. Theoretically, he argued that if the willingness to make concessions is a function of relative capabilities, then restricting the flow of arms would impact the willingness to accept mediation offers. He also argued that the standards for sanction success are too narrow and he concluded that, if judged by the outcome of forcing the targeted state to change a policy, arms embargoes have a rather low rate of success (8% by his count). However, his results also demonstrated that those sanctions imposed specifically to end civil wars were the most likely to achieve their policy goals. A central conclusion of the study, according to Brzoska, was that ‘arms embargoes in and of themselves will seldom affect target policies. They are instead most effective when utilized as a consistent element of larger policy packages’ (Brzoska, 2008: 24).

Gershenson (2002: 190) argued that it is possible for costly sanctions to lower the expected income from victory enough that combatants can generate greater income through negotiations. He argued that once sanctions are imposed, the challenger group has greater motivation to win than the sanctioned group. For example, if the sanctioned group wins, the sanctions continue and the amount of capturable rents is reduced by the continued enforcement of sanctions. However, if the challenger wins, sanctions would be ended, increasing economic output and the availability of rents (presumably to both sides). However, if the sanctioner appears less committed to achieving its desired outcome than the civil war participants, then there is no reason to expect sanctions to continue to affect revenue into the future. Sanctions backed by a strong commitment by the sender are critical to achieving desired outcomes.

Cortright & Lopez (2000) reach conclusions that are similar to those of earlier quantitative work. One strong conclusion that they draw is that ‘comprehensive, rigorously enforced sanctions are more likely to be successful than limited, unenforced measures’ (Cortright & Lopez, 2000: 208). Partial or weakly enforced sanctions were found to be highly unlikely to bring about an end to civil conflicts. ‘The one constant theme was that limited, poorly enforced sanctions had no chance of success’ (Cortright & Lopez, 2000: 208).

In general the extant literature on economic sanctions in civil conflicts suggests that to be successful sanctions need to be comprehensively imposed and enforced. We build on this by arguing that there are two primary reasons that sanctions work to help bring civil conflicts to an end under some conditions but not others. First, in order for sanctions to affect costs they must be adequately enforced. It is not enough to simply legislate sanctions without the ability to enforce the mandated restrictions. Second, sanctions that lack enforcement demonstrate weak resolve on the part of the sanctioning states. When states are not willing to bear the costs of sanction enforcement, the sanctions are exposed as a form of cheap talk. We propose that an effective way to enforce sanctions and show resolve is to couple the imposition of economic sanctions with signals of resolve and the capabilities to enforce them evident in military interventions.

Theoretical framework

We propose two mechanisms through which sanctions can affect outcomes of civil conflicts within a bargaining framework. The first is the enforcement of restrictions that reduce the value of continued fighting and the second is a commitment to maintain restrictions until a dispute is resolved. The key causal mechanism in the effectiveness of sanctions involves costs, to the sender(s) and the target.

Sanctions represent an attempt by one actor – or group of actors – to influence the internal dynamics or interstate relations in another country. Influence attempts can serve to reinforce or change current behavior, as well as manipulate anticipated future behaviors (Singer, 1963; Hufbauer et al., 2007; Morgan & Bapat, 2003). Within the context of an ongoing civil conflict we focus on the role of sanctions in manipulating the current and future costs of actors involved in armed violence. Sanctions can reinforce future behavior if the sanctioner(s) can demonstrate a credible commitment to continue enforcing sanctions until actors change their behavior in a way that is more conducive to the preferences of the sanctioning country – in this case that behavior is ending civil violence. The violence can end via victory, negotiated settlement or stalemate; however, the most effective sanctions can facilitate negotiated outcomes to civil conflicts.

Civil conflicts are fought over a diverse range of issues or conditions, from poverty (Regan, 2009; Rice, Graff & Lewis, 2006), to ethnic divisions (Sambanis, 2001), to opportunity structures (Fearon & Laitin, 2003). A bargaining framework for the onset and duration of civil conflicts would point toward asymmetry of information or non-negotiable demands as core, and mediated negotiations can reduce the asymmetry of information problem. Indeed, previous research on sanctions and civil war has focused primarily on the ability of sanctions to reduce information asymmetries (Strandow, 2006; Escribà-Folch, 2010).

When strong external actors demonstrate their commitment, sanctions can reduce information asymmetries by altering beliefs about the capabilities of actors in civil conflicts. Sanctions can be a powerful signal of actual levels of external commitment (Kaempfer & Lowenberg, 1992), in part because they help separate committed states from those engaging in cheap talk. If powerful states and international organizations refuse to join a sanctions regime, or fail to commit resources to their enforcement, then sanctioners signal weak commitment despite rhetoric by external actors about a commitment to end a civil conflict. However, when international organizations or major powers impose sanctions and commit the resources necessary to enforce them, it can be a strong signal of commitment to ending the civil conflict. This can help solve informational problems, particularly when conflicting sides are relatively equally matched in material capabilities. One approach to doing this is through the combination of sanctions with military interventions that serve as a signaling and enforcement mechanism.

Costs to the targeted state, both anticipated and current, are a function of the scarcity generated by sanctions and the expectation that this level of scarcity will endure. The commitment of the sender influences this expectation. The ability to circumvent sanctions also influences contemporary and expected costs, and to the extent that the sender can increase these costs, compliance by the target is more likely. But there are also costs to the sender from imposing sanctions and to the degree that sanctions can be circumvented or the domestic costs of imposition increase, the likelihood of compliance decreases because the sender has to incur greater costs for compliance. From this perspective, costs to the sender from sanctions can be low and the ‘real’ costs to the target high. This builds an incentive to circumvent on the part of the target, and if political costs increase for the sender there is an increased incentive to rely on symbolism rather than enforcement. This bargaining among actors leaves the target in a strong position.

If commitment and enforcement were cheap, the ability to circumvent would be low and the expectations of recurring costs from sanctions to the target high. Enforcement and commitment by the sender is costly, however. Our argument about coordination and intervention turns on the notion that when costs increase to the sender, the target has fewer degrees of freedom to reduce current and anticipated costs. Contemporary scholarship does not propose a strong relationship between sanctions and the management of civil war, even though it is a frequent event. Institutionally imposed – or coordinated – sanctions, however, have a more successful record (Escribà-Folch, 2010). We argue that in the bargaining between sender and target, the sender must increase its costs in order to demonstrate to the target its commitment. Military intervention and internationally coordinated sanctions are mechanisms to achieve this objective. Interventions outside the context of international sanctions operate quite differently – that is, we see sanctions and interventions to have an interactive effect and this interactive effect would have a greater impact on motivating successful negotiations than a military victory.

Interventions without sanctions are a mechanism to influence relative capabilities and through this, civil war outcomes (Regan, 1996). The evidence, however, demonstrates that they tend to increase the duration of civil wars (Regan, 2002; Balch-Lindsay & Enterline, 2000). Military interventions implemented in conjunction with economic sanctions also serve this independent process of manipulating the relative capabilities, but, we argue, they are also seen as a leverage point for the sanctions themselves. Put differently, military interventions can operate as a tool of sanction enforcement and a demonstration of resolve somewhat independently of their role in balancing capabilities. Moreover, different forms of interventions implemented concurrently can be thought of as part of a strategic process whereby one is designed to complement the other (Aydin & Regan, 2012). We focus more directly on this role of supporting sanctions than in balancing capabilities as it plays out through enforcement and commitment.

Enforcement difficulties

Sanctions can provide material incentives for warring factions to seek an end to civil wars, but they may still be limited in their effectiveness by enforcement difficulties. An inherent difficulty in enforcing sanctions is that if the demand for sanctioned goods does not diminish, then tough sanctions that limit the supply of goods will produce an increasing incentive for black markets to develop to supply the goods at increased prices. Thus, while sanctions can increase the costs of acquiring certain goods, they often do not block the flow of goods at higher prices. Actors committed to violence may be willing to pay almost any price to obtain a material advantage over their adversary in a civil war. Put differently, sanctions can be costly to the target.

Keeping sanctioned goods from being delivered to the targeted country via black markets or by countries that violate the sanctions requires active enforcement. If sanctions only affect the cost of acquiring the good then this might not be sufficient to generate movement toward settling a civil war because the expected value of victory changes only marginally. Sanctions that have the ability to cut off the supply of goods, even when incentives to supply the goods increase, will have a greater influence on the willingness of civil war combatants to make concessions. But enforcement can be costly to the sender.

Enforcement can take on many dimensions, particularly in the banking and finance centers, but in the context of a civil war, this can be most effectively implemented through the concurrent use of military interventions. That is, enforcement can be greatly enhanced by the presence of an intervening force in support of the sender’s objectives, and sanctions imposed without an accompanying military intervention are less likely to compel civil conflict participants to negotiate. Military interventions used in an enforcement role might include active maritime or land interdiction, air patrols of clandestine supply routes, intelligence gathering on the ground, or active engagement against the smuggling of contraband. We saw this, for example, in the enforcement of the arms embargo in the Bosnian conflict in the early 1990s.

Thus, sanctions qua sanctions might be insufficient to motivate alternative future behavior. Instead the strength or comprehensiveness of actions by outside actors would be a mediating condition. Put differently, the acceptance of a seat at the negotiating table in the norm implies that there is at least a set of possible conditions short of victory to which each side will agree. With a strong sanctioning regime, that set of possible conditions might exist, but it may still be too close to an actor’s ideal point to motivate participation. However, when the sanction regime imposes significant costs (or benefits) and can help constrain a regime or diminish the ability of opposition forces to attack the current government, then the value of continued fighting could be less appealing than possible negotiated outcomes (Morgan, 1984). This would hold even if underlying grievances remain unresolved. Militarily enforced sanctions might not have the ability to shift material capabilities sufficiently to generate victory, but in combination, strong military interventions and economic sanctions can make the value of victory less than a possible range of outcomes achieved at the negotiating table. Being squeezed by increasing costs, constrained by military force, and offered an opportunity to negotiate, targeted states would be more likely to negotiate than fight.

This interplay between military intervention as enforcement and military intervention as a participant in a civil war might account for discordant empirical results in the literature. The interactive effect of coupling sanctions with a military intervention generates a costly signal and operates as an influence attempt where the whole is greater than the sum of its parts.

The commitment to maintain sanctions

Even if sanctions impose restrictions that make a negotiated settlement preferable to continued hostilities, they may still fail to bring disputants to the negotiation table if the sides in the conflict believe that the sanctions are temporary. Giving up current strength for a promise of future rewards is risky, particularly if there is an expectation that the conditions under which the agreement is preferable cannot be maintained into the future. Restrictions imposed by sanctions do very little to change the underlying incompatibilities at the core of civil conflicts (Nincic, 2005). Thus, even if sanctions are successful at restricting resources and increasing the short-term costs of fighting relative to peace, they will be unlikely to change the behavior of actors unless they believe that these restrictions can, and will, be maintained into the future. Therefore, sanctioners must demonstrate a commitment to maintain sanctions as long as necessary.

Consider that civil war participants have already decided to trade the present value of peace for the expected value of conflict. Sanctions can alter the expected probability of emerging victorious in a conflict by showing support for one side in a conflict, thus helping to resolve informational asymmetries. However, if sanctions are expected to be maintained into the future if the sender’s preferred side is not victorious, then they can also alter the future value of winning or losing a conflict. If sanctions are strong enough and the consequences of a negotiated settlement are minimized, then a negotiated settlement may be more valuable than ‘winning’ under conditions of continued sanctions. Cuba is an example, where the side that emerged victorious had its value for victory severely impaired for decades as the result of continued economic sanctions. We also might see this in Syria if the Assad regime were to win and Assad were to retain power.

If opposition forces believe that continued conflict will take place in spite of economic restrictions, then a negotiated outcome today may be preferable to continued fighting with the hope of winning a diminished prize later. In this case, the most important elements of sanctions would be the ability to enforce restrictions, and the perception that the senders have the resolve to continue to enforce them until an agreement is reached. Pirani’s (2010) case study of the effect of sanctions on the warring factions in Yugoslavia in the 1990s demonstrates how these mechanisms have worked in the past. He concluded that the perceived asymmetry of motivation in favor of the sanctioning coalition played an important role in bringing about an end to the conflict. In effect, he argues that it became evident to all involved that the sanctioning coalition had the resolve to maintain sanctions until their desired outcome was achieved. As the enforcement ability and commitment of the interveners was revealed to be as great as the participants’, negotiating in the present began to look more favorable than the possibility of victory in the future. From a different perspective this might be what diminishes the impact of sanctions in Syria. Without any firm commitment to maintain pressure on the Assad government, neither side has much of an incentive to negotiate. In the early stages of the conflict, for example, the opposition allied with the USA refused to participate in negotiations even though the Assad government agreed.

The communication of resolve is one of the most difficult problems for states involved in conflicts (Baldwin, 1985) and is a fundamental concept in theories of international relations based on a bargaining framework. One way for states to demonstrate resolve is by taking costly measures that unresolved states would not take. Sanctions can be a costly form of conflict escalation, but are frequently imposed at very low costs to the sender state, leaving their targets to question whether sanctions are a sign of resolve or a half measure designed to satisfy domestic and international audiences without incurring substantial costs (Hufbauer, 1998).

Commitment can be demonstrated through broadly organized sanctions – such as those against Iranian nuclear efforts – or by military interventions. Military interventions generally require the movement of personnel and equipment, and the provision of supplies to support these personnel. This comes at a greater cost to the sender and demonstrates a greater degree of resolve on the part of the sender nation than sanctions alone. Interventions also can put interveners’ military personnel in harm’s way, and the willingness to do so demonstrates commitment. Thus, one way for states to demonstrate their commitment to maintaining restrictions on civil war participants is through the deployment of force to enforce sanctions. In this way military interventions serve dual purposes of influencing the relative balance of capabilities and demonstrating resolve with regard to the imposition of sanctions – and each of these alone has at best a weak record of ending civil wars. But importantly, when military interventions are used in conjunction with internationally imposed sanctions, we see that their primary contribution is buttressing the sanctions rather than an independent effort to manipulate relative capabilities.

While all military interventions have the ability to convey the resolve of outside actors, interventions by major powers have greater potential to impose high costs and to sustain interventions over a long period of time if necessary. Thus, major power state involvement increases the credibility of the intervening states to sustain the intervention for a long period. This leads us to expect that when major power states intervene militarily in conjunction with sanctions, the expected duration of civil conflicts will be decreased.

Alternatively, states can show resolve in sanctions by demonstrating broad political support through the inclusion of international organizations in the sanctioning body. International agreement on a sanctions regime requires coordination beyond the imposition of unilateral sanctions (Martin, 1992). Thus, the presence of sanctions by an international institution is a politically costly measure that should both increase the capability to enforce sanctions and demonstrate the resolve of the sending countries to maintain sanctions into the future (Martin, 1992). International institutional involvement can also help coordinate the resources of the sanctioning states, providing commitment beyond unilateral actions. All of these elements can help increase the ability of the sanctions to impose meaningful costs and to maintain the imposition of those costs for a sustained period of time if necessary.

In this section, we have provided two mechanisms that have reinforcing implications: a commitment and an enforcement mechanism. In combination, these policies should lead to more effective efforts at bringing civil conflicts to an end. Sanctions alone are insufficient for demonstrating commitment because they can be relatively costless to the sender and they are not self-enforcing. Sanctions that are imposed through an international institution are costlier for states to impose and should represent an increased commitment on the part of the senders. Institutionally imposed sanctions that are accompanied by a military intervention, particularly if the intervention involves a major power, will maximize levels of commitment and enforcement and are expected to have the greatest effect on civil war outcomes.

Hypothesis 1: International institutional involvement in sanctions in combination with a military intervention will decrease the expected duration of civil conflicts.

Civil conflicts could end for a number of reasons. Victory, stalemate, and negotiated agreements provide the general categories by which they end. Sanctions by themselves might neither convey the gravity to influence victory or defeat nor impose costs in a time frame under which victory could be reasonably linked to their imposition. If the primary way that sanctions are influencing the duration of civil conflicts is by increasing the costs of continued fighting, then we would expect them to have the biggest effect on bringing about negotiated settlements between the warring factions.

Our theory expects that institutionally imposed sanctions that are implemented in conjunction with military interventions will motivate a negotiated end to a civil war. The sunk costs of war are hard to overcome through the narrow manipulation of capabilities, either military or financial, but the conjunction of military enforcement, economic hardship, and future expectations can help shape negotiated outcomes. To suggest that economic sanctions affect the chance of military victory puts significant weight on a causal mechanism ill-suited for the proposed outcome. Only under the most limited set of conditions would the economic cost of sanctions generate a military collapse. But sanctions and their enforcement can increase the cost of a continued military strategy relative to the range of possible negotiated outcomes. Thus, we expect that when sanctions are imposed by an international institution and are accompanied by a military intervention, the likelihood of the civil conflict ending in a negotiated settlement compared to ending in a victory or due to low activity will increase significantly. More formally:

Hypothesis 2: Internationally imposed economic sanctions supported by a military intervention increase the likelihood that a civil conflict will end in a negotiated settlement.

Research methods and data

To test our hypotheses we use data for the years 1950–2005. Our unit of analysis is the civil conflict country-month. To test expectations about the effect of sanctions and military interventions on conflict termination, several binary time-series cross-section (event history) models are estimated. The dependent variable in these models measures the end of a civil conflict as identified by the Uppsala Conflict Data Program (UCDP) Armed Conflict Dataset (Themnér & Wallensteen, 2015). The termination of civil conflicts is indicated using a dummy variable coded 1 in the month that the civil conflict ends and 0 if it continues in the month. The event history methodology used in this article is an alternative to estimating survival models that can be used with time-series cross-section data with a binary dependent variable. Building on Beck, Katz & Tucker (1998), Marinov (2005: 570) uses this technique in modeling the effect of sanctions on leadership survival and provides a concise summary for why a properly specified logit model is technically equivalent to a survival model.

To test expectations about how civil conflicts end, data from Kreutz (2010) are used. We combine Kreutz’s six types of conflict outcomes into a conceptually similar four-category variable for use as a dependent variable in a multinomial logit model. This variable codes conflicts as continuing, ending in negotiated settlements (when the two sides sign a peace agreement or negotiate a ceasefire), victory, or ending in low activity. These models use the same set of control variables as in the civil conflict termination estimations.

Independent variables: Military and economic interventions

Our theory proposes that when interveners are more credible in their commitment and have the ability to enforce and maintain sanctions, there are additional incentives for the warring sides in a civil conflict to find a solution that brings the conflict to an end. Our primary independent variables operationalize two main measures of enforcement and commitment: the presence of economic sanctions imposed by international institutions and the presence of military interveners in a civil conflict. Data on economic sanctions come from version 4 of the Threat and Imposition of Economic Sanctions (TIES) dataset (Morgan, Bapat & Kobayashi, 2014). Our theory focuses on effects of imposed sanctions, so we first remove any cases where there were threats only. We then generate a dummy variable coded 1 for the involvement of an international institution in the sanctioning coalition.

Military interventions are identified in the UCDP dataset and are defined in terms of states entering a conflict with troops to actively support the government or the opposition (UCDP/PRIO Armed Conflict Dataset Codebook, 2013: 7, 8). To ensure maximum coverage of all interventions, these data are supplemented with cases from the International Military Interventions (IMI) dataset (Pickering & Kisangani, 2009) and the Military Interventions by Powerful States (MIPS) dataset compiled by Sullivan & Koch (2009). A dummy variable for major power interventions is also coded using data from the MIPS dataset, which identifies all interventions involving major power states.

Control variables

Following Achen (2002, 2005), we try to minimize the number of control variables appearing in our models while still including those which may be correlated with the independent and dependent variables (King, Keohane & Verba, 1994; Ray, 2003). We control for characteristics of the conflict country as well as the severity of the conflict.

Regime type, development, and the size of the population are characteristics of the conflict country that are controlled for in all of the models estimated. Regime type has been shown to be correlated with sanctions imposition and success (Kirshner, 1997; Lektzian & Souva, 2003) and has been included in other models of civil war duration (e.g. DeRouen & Sobek, 2004; Collier, Hoeffler & Söderbom, 2004). We operationalize democracy using Unified Democracy Scores from Pemstein, Meserve & Melton (2010). Civil wars in countries with higher levels of development, as measured by income, tend to be shorter (e.g. DeRouen & Sobek, 2004; Collier, Hoeffler & Söderbom, 2004), while wealthier countries also have more resources to draw on, making it harder for sanctions to impose significant costs on leaders. Larger populations have been found to be associated with longer civil wars (Collier, Hoeffler & Söderbom, 2004), and as with economic resources, human resources in the form of larger populations could negatively affect the success of sanctions (see Hegre & Sambanis, 2006). Wealth and population are operationalized using logged GDP per capita and logged population data from Gleditsch (2002).

We also control for the intensity of civil conflicts with a variable that takes the value 1 when the conflict has at least 1,000 battle-related deaths in a given year (UCDP/PRIO Armed Conflict Dataset Codebook, 2013). These conflicts are likely to be longer and harder to influence with the use of sanctions. To account for time-series dynamics, a cubic polynomial of time is also constructed using the number of years that a country has been involved in a civil conflict and its squared and cubed terms (Carter & Signorino, 2010). Additionally, the potential for non-independence between countries is accounted for by clustering the standard errors by the country. Finally, when estimating the effect of specific types of sanctions – for example, institutional sanctions – a dummy variable is included for the presence of other types of sanctions – in this example, non-institutional sanctions. This shifts the reference category to ‘no sanctions’, rather than ‘no sanctions and sanctions that did not include an international institution’. We also use this specification when estimating the effect of interventions by major powers.

Results

Table I contains the main findings of our empirical analysis of the effect of sanctions and military interventions on the ending of civil conflicts. The models in Table I are all estimated using a random effects logit estimator with standard errors clustered on civil conflict countries.³ We first turn to Models 1 through 4 of Table I. By using dummy variable interactions, the results of these models can be manipulated to reveal the effect of unilateral sanctions with and without military interventions or major power military interventions (Models 1 and 3), and the effect of institutional sanctions with and without military interventions or major power military interventions (Models 2 and 4).

Looking first at the lower-order terms of the interaction effects in Models 1–4, we see that sanctions, whether they are imposed unilaterally or with the support of an international institution, have a generally positive but insignificant effect on bringing civil conflicts to an end when they are not accompanied by military interveners. While our argument would imply the possibility that moving from unilateral sanctions to institutional sanctions would increase both the enforcement capabilities of sanctions and the commitment to maintain the sanctions, empirical evidence indicates that without the presence of military interveners this is not enough to significantly shorten the duration of civil conflicts. Because this finding appears to contradict previous work showing that institutional sanctions shorten the duration of civil conflicts (Escribà-Folch, 2010), we re-estimated Models 1–4 without the inclusion of the interaction term. Without the interaction term, we found that controlling for military interventions, institutional sanctions do increase the likelihood of civil conflicts ending in a given month, while unilateral sanctions do not.⁴ Analyzing the interaction models in Table I allows us to extend these findings by showing that the success of institutional sanctions in bringing civil conflicts to an end is greatly enhanced by the inclusion of military interventions occurring concurrent to the sanctions. Additionally, as noted above, the interaction terms of Models 2 and 4 in Table I show that when military interveners are not present, the significant effect of institutional sanctions found by Escribà-Folch (2010), and replicated here in Table S1b in the Online appendix, disappears.

Looking more closely at the interaction terms in Models 1 and 3 of Table I, we see that when sanctions are imposed unilaterally, the interaction of sanctions and a military intervention (with or without a major power presence) does not significantly alter the duration of civil conflicts. However, the interaction terms in Models 2 and 4, where institutional sanctions are combined with interventions (Model 2) and interventions that include a major power (Model 4), are statistically significant and substantively quite large relative to the lower-order terms.

Table I.

Sanctions, military interventions, and the ending of civil conflicts

Dependent variable: End of civil conflict	Model 1	Model 2	Model 3	Model 4
Unilateral sanctions	0.50		0.16
	(1.63)		(0.59)
Institution sanctions		0.33		0.48
		(0.86)		(1.32)
Military intervention	−0.25	−0.47*
	(−1.30)	(−2.33)
Major power intervention			−0.75	−0.98*
			(−1.59)	(−2.03)
Unilateral sanctions*Intervention	−0.46
	(−1.16)
Institution sanctions*Intervention		0.87†
		(1.87)
Unilateral sanctions*Major power intervention			0.86
			(0.85)
Institution sanctions*Major power intervention				2.02*
				(2.26)
Other sanctions	0.61*	0.41†	0.62*	0.37†
	(2.54)	(1.89)	(2.51)	(1.81)
Other military interventions			−0.31	−0.37
			(−0.93)	(−1.13)
Ln(GDP/capita)	−0.07	−0.07	−0.04	−0.04
	(−0.62)	(−0.57)	(−0.37)	(−0.30)
Democracy	−0.08	−0.07	−0.11	−0.05
	(−0.56)	(−0.48)	(−0.72)	(−0.34)
Major civil conflict	−0.44*	−0.45*	−0.41†	−0.36†
	(−1.97)	(−2.10)	(−1.88)	(−1.72)
Ln(Population)	−0.30*	−0.30*	−0.30*	−0.31*
	(−2.21)	(−2.20)	(−2.14)	(−2.12)
Constant	0.34	0.41	0.10	0.18
	(0.24)	(0.28)	(0.07)	(0.12)
Cubic polynomial of time	Yes	Yes	Yes	Yes
Observations	11,976	11,976	11,976	11,976
Log-pseudolikelihood	−1,262.12	−1,261.58	−1,261.34	−1,259.82
Pseudo R-squared	0.017	0.017	0.017	0.018

Significance levels: **p < 0.01, *p < 0.05, †p < 0.1. Robust z–statistics in parentheses. Estimates are derived from a random effects logit model with standard errors clustered on the country.

In Model 2, evaluating the coefficient on institutional sanctions together with the significant interaction term reveals that when institutional sanctions are supported with a military intervention, the duration of civil conflicts is expected to be significantly shortened (beta = 1.20; z = 2.93). Substantively, adding a military intervention by an international institution to sanctions increases the estimated probability of a civil conflict ending in a given month by approximately 45% (from about 4.2% to about 6.2%).⁵

Model 4 demonstrates that when major powers intervene militarily in conjunction with economic sanctions by international institutions, the likelihood of civil conflicts ending reaches its peak. Including the presence of a major power military intervener, the coefficient on institutional sanctions increases (beta = 2.50; z = 3.00). Substantively, when international institutions impose sanctions and major powers intervene militarily, the estimated probability of a civil conflict ending in a month increases to 12%, four times the baseline of 2.8% for civil conflicts without institutional sanctions or major power interventions.⁶

Figure 1.

Survival function from Cox proportional hazards regression

The findings in Table I support the first hypothesis of this article. When unilateral or institutional sanctions are imposed in isolation, without military interventions, they do not significantly affect the duration of civil conflicts. However, as expected by Hypothesis 1, when sanctions are imposed by international institutions in conjunction with military interventions, civil conflicts are found to be significantly more likely to terminate. As expected, this effect is strongest when the military intervention includes a major power.

A supplementary finding from the coefficients on military interventions and major power military interventions in Models 2 and 4 is that military interventions without the presence of sanctions by international institutions are found to lengthen the duration of civil conflicts. This supports previous work that has found a similar empirical relationship. Evaluating the interaction term in these models shows that when sanctions by international institutions are present the sign on military interventions flips to positive, but does not reach statistical significance. Investigating this relationship further may be a topic for future research and might shed light on the persistent finding that interventions prolong civil conflicts.

In addition to the estimates presented in Table I, for robustness, we estimate a Cox proportional hazards model on the duration of civil conflicts. The Cox model uses the same model specification as Model 2 from Table I.⁷ Figure 1 is a graph of the survival function from that model plotted against civil conflict dispute months over five years for the different categories of the 2×2 interaction of institutional sanctions and military interventions. The duration of those conflicts that experience both institutional sanctions and military interventions is seen to be significantly shorter than those that do not.⁸

Regarding the control variables in Table I, we find that major civil conflicts are expected to last significantly longer than smaller conflicts, and that countries with larger populations tend to experience longer civil conflicts. Wealth and democracy are both insignificantly related to civil conflict endings.

The Models in Table II are designed to provide a test of Hypothesis 2 by investigating the likelihood of civil conflicts ending in different types of outcomes. Table I provides evidence that institutional sanctions and major power interventions, together, can shorten civil conflicts. Table II shows the results of three multinomial logit models that shed additional light on the manner in which sanctions and military interventions can work together to shorten the duration of civil conflicts. Three civil conflict outcomes are considered. The civil conflict can end in a negotiated settlement between the two sides or a victory for one side, or it can dissipate due to low activity. The reference category in Table II is that the civil conflict continues to the next period.

The first thing we note from Table II is that neither unilateral nor institutional sanctions, without accompanying military interventions, have a significant effect on bringing civil conflicts to a close by any of the means considered. This is to be expected based on the results of Table I, which showed that unilateral and institutional sanctions, by themselves, do not significantly shorten the duration of civil conflicts. Looking at the interaction terms, we see that sanctions imposed by international institutions generally show a strong positive interactive effect with military interventions and major power interventions. The interactive effect of unilateral sanctions, on the other hand, is only significant when considering negotiated settlements, and in this case the interaction term is negative.

To get a better substantive feel for what the coefficients in Table II mean, it helps to look at the predicted probabilities of each outcome’s occurrence based on the results of the models. Predicted probabilities for the

Table II.

Sanctions, military interventions, and civil conflict outcomes (multinomial logit)

	Y = 1, negotiated settlement			Y = 2, victory			Y = 3, low activity
Independent variables	(1)	(2)	(3)	(1)	(2)	(3)	(1)	(2)	(3)
Unilateral sanctions	0.51			0.30			0.21
	(0.80)			(0.60)			(0.60)
Institution sanctions		−1.64	−0.51		−0.21	0.32		0.43	0.23
		(−1.48)	(−0.90)		(−0.35)	(0.63)		(1.41)	(0.73)
Military intervention	0.36	−0.10		−0.38	−0.66*		−0.10	−0.13
	(1.10)	(−0.31)		(−1.47)	(−2.51)		(−0.45)	(−0.56)
Major power intervention			−1.81† (−1.68)			−0.16 (−0.35)			−0.53 (−1.09)
Unilateral sanctions*Intervention	−2.67* (−2.11)			−0.90 (−1.02)			0.23 (0.51)
Institution sanctions*Intervention		2.77* (2.34)			1.67* (2.40)			−0.02 (−0.04)
Institution sanctions *Major power intervention			4.36** (2.65)			1.32 (0.90)			1.79** (3.04)
Other sanctions	−0.09	−0.41	−0.45	0.55	0.30	0.27	0.43†	0.50*	0.40*
	(−0.18)	(−0.72)	(−0.80)	(1.48)	(0.87)	(0.80)	(1.71)	(2.27)	(1.86)
Other military interventions			0.10 (0.22)			−0.25 (−0.63)			−0.23 (−0.43)
Ln(GDP/capita)	0.09	0.15	0.12	−0.22	−0.21	−0.18	0.04	0.00	0.05
	(0.62)	(0.94)	(0.73)	(−1.44)	(−1.41)	(−1.18)	(0.43)	(0.01)	(0.54)
Democracy	0.38†	0.28	0.35	−0.31	−0.27	−0.30	−0.46**	−0.46**	−0.43**
	(1.68)	(1.19)	(1.30)	(−1.27)	(−1.11)	(−1.22)	(−2.96)	(−2.96)	(−2.96)
Major civil conflict	−0.41	−0.42	−0.20	−0.02	−0.03	−0.02	−0.33	−0.21	−0.26
	(−1.08)	(−1.15)	(−0.53)	(−0.08)	(−0.11)	(−0.09)	(−1.29)	(−0.82)	(−1.08)
Ln(Population)	−0.44**	−0.44**	−0.42**	−0.25†	−0.25†	−0.23†	0.37**	0.43**	0.36**
	(−3.36)	(−3.34)	(−2.86)	(−1.91)	(−1.92)	(−1.82)	(5.04)	(5.32)	(4.46)
Constant	−0.86	−1.04	−1.17	0.81	0.85	0.29	−8.41***	−8.86***	−8.33***
	(−0.51)	(−0.58)	(−0.62)	(0.47)	(0.50)	(0.17)	(−7.22)	(−7.13)	(−7.08)
Model	1	2	3
Cubic polynomial of time	Yes	Yes	Yes
Observations	11,963	11,963	11,963
Log-pseudolikelihood	−1,401.32	−1,400.21	−1,401.98
Pseudo R-squared	0.09	0.09	0.09

Significance levels: **p < 0.01, *p < 0.05, †p < 0.1. Robust z–statistics in parentheses. Estimates are derived from a random effects logit model with standard errors clustered on the country.

different possible combinations of the 2×2 interaction term appear in Table III. We can begin by comparing the results of Model 1, with unilateral sanctions, to those from Model 2, with institutional sanctions. The first major difference between the duration of civil conflicts with institutional sanctions compared to those with unilateral sanctions is that when institutional sanctions are combined with military interventions the probability of a dispute continuing drops from 97.4% to 95.1%. By comparison, when states impose sanctions unilaterally and a military intervention accompanies the sanctions, the probability of the dispute continuing into the next month does not decrease.

The second major difference, which pertains directly to Hypothesis 2, is that the probability of a civil conflict ending in a negotiated settlement increases from 0.6% without sanctions by an institution or a military intervention to 1.6% when both are present. By comparison, the probability of a civil conflict ending in a negotiated settlement decreases from 0.4% without unilaterally imposed sanctions or a military intervention to just 0.1% when both are present. The only outcome to

Table III.

Sanctions, military interventions, and estimated probabilities of different civil conflict outcomes in a month

	Y = 1, Neg. settlement			Y = 2, Victory			Y = 3, Low activity			Y = 0, Continues
Independent variables	(1)	(2)	(3)	(1)	(2)	(3)	(1)	(2)	(3)	(1)	(2)	(3)
No sanctions, no intervention	0.5	0.6	0.6	0.8	0.9	0.7	1.1	1.1	1.1	97.6	97.4	97.7
Unilateral sanctions	0.8			1.1			1.3			96.8
Institution sanctions		0.1	0.3		0.7	1.0		1.6	1.4		97.6	97.3
Military intervention	0.7	0.5		0.6	0.5		1.0	1.0		97.7	98.0
Major power intervention			0.1			0.6			0.6			98.7
Unilateral sanctions*Intervention	0.1			0.3			1.6			98.0
Institution sanctions*Intervention		1.5			1.9			1.6			95.1
Institution sanctions*Major power intervention			4.0			2.6			4.3			89.3

increase in probability when unilaterally imposed sanctions are supported by military interventions is the low activity outcome (although this coefficient is not statistically significant in Model 1 of Table II). Thus, when civil conflicts do come to an end after unilateral sanctions and military intervention, it does not appear likely that this is because of the interveners helping the two sides reach a negotiated settlement or one side to achieve a decisive outcome.

When international institutions are involved in the imposition of sanctions in conjunction with military interventions (Model 2), the probability of civil conflicts ending by all types of outcomes increases as the probability of the conflict continuing decreases.⁹ As expected in Hypothesis 2, the probability of a civil conflict ending in a negotiated settlement increases the most, with a substantive increase of over 150% (from 0.6% to 1.6%) and statistical significance at the .05 level.¹⁰ The probability of the conflict ending in a victory by one side is also substantively and statistically significantly increased¹¹ (the predicted probability more than doubles from 0.9% to 1.9%) when institutional sanctions are imposed in conjunction with a military intervention.

Model 2 considered the conditional effect of institutional sanctions with and without military interventions. In Model 3, the interactive effect of institutional sanctions and major power military interveners are considered, rather than all military interventions. The predicted probabilities from Model 3 show that the likelihood of a civil conflict continuing into the next month reaches its nadir (89.3%) when international institutions impose sanctions in conjunction with a major power military intervention. Additionally, when major powers are involved in the military intervention, we see an even larger increase in the probability of civil conflicts ending in negotiated settlements. This probability rises from 0.6% when neither institutional sanctions nor major power interventions take place, to 4.0% when institutions sanction and major powers intervene.

Our results present strong evidence that civil conflict participants are influenced by costs of sanctions and the credibility of their continued implementation. When the intervention includes a major power and the sanctions include the participation of international institutions, the estimated probability of a negotiated settlement is strongest, indicating that the enhanced credibility of these policies can cause actors to discount the utility of future benefits from continued fighting and come to the negotiation table.

Conclusion

Economic sanctions are frequently imposed on countries involved in civil conflicts, but relatively few academic studies have attempted to understand the conditions under which sanctions can affect civil conflict outcomes. Previous research has been divided on whether sanctions hasten or delay the end of these conflicts. This article advances the literature on economic sanctions by estimating the effect of sanctions on civil conflicts when they are imposed with and without accompanying military interventions.

Importantly, our results highlight the critical role that international institutions can play in coordinating, moderating, and resolving domestic conflicts. Absent the coordinated efforts at the institutional level, our results provide scant support for the effectiveness of sanctions, but when the international community acts in concert the importance of sanctions as a form of conflict management is elevated.

Institutional coordination over a sanction regime, however, is not sufficient for increased effectiveness over unilateral sanctions. For example, our results demonstrate that institutional sanctions, when imposed without complementary military support, will not significantly increase the likelihood of civil conflict termination. However, our research supports the expectation that institutional sanctions can be more effective when combined with military interventions, particularly those that include the presence of a major power. In these cases we estimate a substantively large increase in the probability of civil conflicts ending in a negotiated settlement. This outcome provides support for the theoretical expectations that were developed based on an application of bargaining theory.

Unfortunately, from a policy perspective, what seems to work best is the strategy that is not often implemented. One role of social science is to uncover relationships that obtain in our referent world; another role is to point toward practical solutions that are built on empirical evidence (Singer, 1985). In our case we have a world that employs strategies such as weak unenforced sanctions, or military interventions that do not include comprehensive economic restrictions, that are not often successful. We see the links to failed interventions as built into the economic and military policy that generates these actions. Our empirical modeling demonstrates rather robustly that a comprehensive sanction regime, implemented in conjunction with a military intervention, makes success more likely. The fact that our referent world does not supply an abundant number of observations speaks to the infrequent link between scholarship and policy. When sanctions are credibly imposed by international institutions, with strong enforcement mechanisms in place and a demonstrated commitment to maintain that presence, participants in a civil conflict have a significantly increased probability of reaching a negotiated settlement to their dispute. When the world community does it ‘right’ we expect the results to be better.

Footnotes

Replication data

The dataset, codebook, and do-files for the empirical analysis in this article, as well as the Online supplemental appendix, can be found at .

Acknowledgements

We would like to thank the International Studies Association for facilitating the workshop that initiated this project. We also thank Cooper Drury, Clifton Morgan, and the participants of the Economic Sanctions Workshop at Rice University, Houston, TX, for helpful comments and suggestions. Vytautas Kuokštis read and provided helpful comments on an earlier draft of the article. We owe special thanks to Lisa Hultman and Dursun Peksen for fruitful discussions on the topic early in the process.

Notes

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