External intervention and civil wars

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Barbara F. Walter

University of California, San Diego

  1. Security Guarantees as Deterrents to Spoilers

I’m going to start with a short discussion about security guarantees in civil wars and then quickly move onto the issue of external intervention more generally. (I’ll explain why in a moment.)

Regarding security guarantees, a strong statistical relationship exists between promises by a third party to enforce or verify civil war peace settlements and their successful implementation. This relationship was first found by Walter (1994, 1997, 2002), and then confirmed by Doyle and Sambanis (2000), Hartzell, Hoddie, Rothchild (2001); Fortna (2002), and Hartzell and Hoddie (2003). If an outside state or international organization is willing to step in to enforce or verify the terms of a peace treaty, negotiations almost always lead to peace. If outsiders do not enforce or verify terms, negotiations almost always result in renewed war. This appears to be because credible guarantees on the terms of an agreement are almost impossible to design by the combatants themselves.
Outside security guarantees are not the only factor necessary to successfully resolve civil wars in a negotiated settlement. A high number of battle deaths, a particularly long war, and a military stalemate are important in convincing combatants to initiate negotiations, and an outside mediator is then influential in getting them to sign a bargain. But by far the best predictor of whether combatants will sign and implement a peace agreement is the willingness of an outside state or international organization to verify or enforce the terms (Walter 2002).
Security guarantees, however, are a very specific type of intervention targeted at a very specific outcome – the signing and implementation of a civil war peace treaty. Looking at this particular relationship tells us nothing about the many different types of intervention that affect decisions by the government and rebels throughout a conflict. Since the relationship between intervention and civil war is an area of potential great scholarly growth, and since there is little understanding and agreement of the mechanisms driving this relationship, I’ve decided to focus the bulk of this memo on this more general subject. My goal is to summarize the quantitative literature on intervention in civil wars, and in the process try to clarify what we know, what we don’t know, and what we should be trying to figure out.
To date, the quantitative work on intervention in civil wars falls into three camps: those that focus on the effects of different types of intervention on civil war duration, those that focus on resolution, and those that focus on the post-war peace. What follows is a brief and imperfect summary of each of these camps.
1. Outside Intervention’s Effect on Civil War Duration.
The relationship: Quantitative studies on the effect of outside intervention on civil war duration have found a strong positive relationship between intervention and how long a civil war lasts (Regan 2000, 2002; Elbadawi and Sambanis 2000). It doesn’t appear to matter whether outside intervention is in the form of direct force, military aid, or economic aid/sanctions, or whether intervention is designed to favor the government, the opposition, or be neutral. Each type of intervention appears to make civil wars last longer (Regan 2000, 2002). As for duration, the longest wars tend to occur when two outside states intervene on opposite sides (Regan 2002). The only type of intervention that tends to shorten a conflict is when an outside state intervenes militarily and economically in favor of the government (Regan 2002). Intervention in these cases appears to help the government defeat the rebels more rapidly than it would otherwise have been able to do.
The measure: Both the Regan (2002) and the Elbadawi/Sambanis (2000) studies rely on Regan’s (2000) definition of external intervention. Regan defines external intervention as intervention by one foreign government in the internal conflict of another using military, economic or mixed means. Military intervention can include troops, supplies, intelligence, or aid. Economic intervention can include sanctions or embargoes, or the granting or withdrawal of aid that affects the costs of engaging the enemy. Elbadawi and Sambanis attempt to address the potential problem of endogeneity by looking at factors associated with external intervention. They find that external intervention is more likely in deadlier wars and when the government side is more democratic. Intervention is less likely in ethnic wars, in regions with many democratic governments and when the state has a strong military.
The interpretation. Regan interprets these findings as indicating that external intervention plays an important role in the cost/benefit calculations of the government and rebels. Outside intervention tends to increase the duration of civil wars because it enhances expectations about victory and lowers the costs of continuing to fight. Groups on the receiving end of outside assistance believe they are more likely to win a war, and at a lower cost, making settlement less attractive.
Elbadawi & Sambanis have a slightly different interpretation. Building on work by Elbadawi (1999) they argue that external intervention in favor of the rebels may lead to longer wars because it allows these groups to better organize and sustain themselves, making military defeat at the hands of the government more difficult.
2. Outside Intervention’s Effect on Civil War Resolution
The relationship: Although external intervention during a civil war tends to prolong a conflict, outside intervention that occurs after a peace treaty has been signed has a strong positive effect on the successful resolution of these wars. In particular, Walter (2002) found that once combatants had agreed to initiate negotiations, an outside mediator, and a third party security guarantee were critical in reaching and signing a comprehensive peace agreement. Once a peace agreement was signed, a third party security guarantee was the best predictor of whether that agreement would then be implemented. In separate studies Doyle and Sambanis (2000) found that third party enforcement can help end violence, while Hartzell, Hoddie, Rothchild (2001); Fortna (2002), and Hartzell and Hoddie (2003) found that the presence of third-party enforcer significantly increased the duration of the peace once a settlement was signed.
The measure: Walter defined a third party security guarantee as offer by an outside state or international organization during negotiations that met two criteria: (1) it had to be a verbal or written promise to verify or enforce post-treaty behavior once a settlement was signed, and (2) the outside state or international organization had to follow through with its promise and provide the expected services. Once again, there was concern that the outside guarantee was merely offered in those civil wars that would have ended in successful negotiated settlements without any outside help. In order to test whether security guarantees had an independent effect on adversaries’ decision to sign and implement peace treaties, Walter (2002) treated third-party guarantees as the dependent variable and performed a logit analysis to see if any of the other factors relevant to the resolution of civil wars predicted the presence of this variable. This test showed that none of the other factors associated with civil war resolution predicted when outsiders would intervene and when they would not.
The interpretation: Walter (1994, 1997, 2002) argues that civil war combatants cannot credibly commit to the terms of peace agreements that create easy opportunities for post-treaty exploitation. In particular, the process of post-treaty demobilization makes combatants especially hesitant to move forward without outside guarantees for their safety. Only in the presence of third party security guarantees do promises to adhere to the terms of a treaty become credible, and implementation likely.
3. Outside Intervention’s Effect on Peace Maintenance
The relationship: External intervention also tends to have a positive effect on reducing the risks of an additional civil war once the first war has ended (Doyle and Sambanis 2000, Fortna 2002). Doyle and Sambanis (2000) find that on the whole, only UN multidimensional peacekeeping operations have a positive effect on bringing peace and increasing democracy in the aftermath of civil war. The probability of successful peacebuilding increases with the deployment of a peacekeeping mission which includes a mandate for economic reconstruction, institutional reform and election oversight. All other types of intervention that take place after wars end (monitoring or observer missions, economic reconstruction/institutional reform, and peace enforcement) appear to have no effect on either the duration of the post-war peace or democratization. In a preliminary study, Fortna (2002) finds that all types of peace-keeping operations listed above have a positive effect on peace maintenance, but she finds this effect only in the post-cold war era.
The measures: Doyle and Sambanis (2000) look at two dependent variables, lenient peacebuilding (which required no violence for two and five years after the war), and strict peacebuilding (which also required an improvement in the democracy score of 3 or greater). Their measures of intervention included four categories:

  1. monitoring or observer missions, where the observers monitor a truce and negotiate a peace settlement. It must be consensual.

  2. Traditional peacekeeping, which includes a mix of strategies including economic reconstruction and institutional reform. It must be consensual.

  3. Multidimensional peacekeeping, which includes a mix of strategies including economic reconstruction and institutional reform. It must be consensual.

  4. Peace enforcement, which includes armed units imposing the peace. May or may not be consensual.

Fortna’s (2002) dependent variable is the number of years of peace after the previous civil war ended. She relies on Doyle and Sambanis’ (2000) categorization of peacekeeping. Fortna takes the extra step of attempting to establish the direction of causality. She finds that peacekeeping missions are less likely to be sent to countries where one side won a military victory, and where the government’s forces are stronger. Non- UN peacekeeping missions were also more likely to go be sent to states that were previously democratic, and less likely to intervene in longer-lasting conflicts.

The interpretation: Doyle and Sambanis (2000) suggest that multidimensional peacekeeping can aid with institutional and political reform, although the exact linkages are not well-developed. Fortna (2002), identifies three possible mechanisms, arguing that peacekeeping (1) increases the costs of renewed aggression, (2) reduces information problems (regarding compliance), and (3) enhances enforcement which then makes commitments more credible.
There has been a profusion of qualitative studies over the last ten years that focus on various aspects of civil war and ethnic conflict, many of which include at least a section on the effects of international intervention. Below is a list of many of the causal mechanisms that have been identified in this literature, as well as mechanisms that might be applicable.
1. External Intervention and Civil War Duration
As we learned from the quantitative studies above, external intervention in the form of military or economic aid offered during a war tends to prolong it. The most popular explanation in the qualitative literature for this relationship is similar to the one offered by Regan (2002) - expected utility. Lake and Rothchild (1998), for example, argue that outside intervention provides the resources necessary for one or both sides to prosecute a war, and can make the players optimistic about the likelihood of a military victory. Both factors can make settlement less attractive.
But three additional mechanisms are also applicable. The first has to do with opportunity costs. Outside intervention in the form or military or economic aid can directly benefit one or both sides, creating incentives for the leaders to pursue war for its own sake. This is an adaptation of the Collier and Hoeffler (2001) opportunity cost argument. The second mechanism has to do with commitment problems. Outside intervention can also prolong civil wars because it makes it difficult for the side that benefits from outside assistance to credibly commit to the terms of a treaty. (For related arguments see Fearon (2004), and Salehyan (2004).) A third mechanism has to do with the number of veto players involved in the bargaining. Cunningham (2004), for example, has argued that the greater the number of veto players on the government and rebel sides, the more difficult it will be for all those involved to reach a mutually agreeable bargain, and the longer a war. The mechanisms he points to are the dual problems of cycling, and hold-out that emerge when multiple parties attempt to compete for favorable terms.
2. External Intervention and Civil War Resolution
A number of arguments have been offered in the qualitative literature for why external intervention would make negotiated settlements more likely. Four of the mechanisms are outlined below.

  1. Expected Utility. Zartman (1989) has argued that civil wars are unlikely to end in negotiated settlements without first experiencing what he calls a “hurting stalemate.” Otherwise, one or both sides might hold out hopes of eventually winning the war at an acceptable cost. Outside intervention can be instrumental in creating such a stalemate and setting up incentives to negotiate.

  2. Information problems. Zartman (1989, 1995), Brown (1996), Lake and Rothchild (1998), and Doyle, Johnston & Orr (1997) have all argued that international mediators can help combatants reach a bargain and thus reduce the duration of a civil war. The mechanism these authors point to are the information problems that tend to arise during the give-and-take of negotiations. Outside mediators can help overcome potential information failures by facilitating communication, clarifying objectives, bringing transparency and legitimation to the proceedings, and changing perceptions of the likely outcome of war. The better the information, the more likely combatants are to reach a settlement, and the shorter the war.

  3. Commitment Problems. The qualitative literature has also recognized the importance of outside intervention in solving various implementation problems. Brown (1996), for example, argues that international monitors can aid in transparency, making cheating less likely. Lake and Rothchild (1998) argue that outside intervention can restore the internal balance of power in the immediate aftermath of a war, and restrain a potentially threatening adversary. They also argue that outside intervention can offer critical protection and enforcement during treaty implementation, making commitments to a settlement more credible (see also Hampson (1996)).

  4. Divisibility. The final mechanisms has to do with an intervener’s ability to make side-payments and to pressure groups and allies to make the concessions necessary for agreement (Lake and Rothchild (1998), Doyle, Johnstone & Orr (1997), Zartman (1995)).

3. External Intervention and Peace Maintenance
At least two qualitative studies address the relationship between external intervention and peace maintenance, although neither study carefully develops the causal links between the two variables. According to Stedman and Rothchild (1996) and Paris (1997) peace-builders provide “financial humanitarian, technical and administrative assistance, and monitor the parties’ compliance with the peace settlement.” The microfoundations of this theory are not developed.
Although the literature on external intervention and civil war has made rapid gains in the last few years, there are still areas for growth.

  1. Direct versus indirect intervention. Current studies have focused on direct intervention and not the numerous indirect ways that outside countries can affect the onset, duration and resolution of civil wars. Gleditsch (2003), for example, has found that the risk of civil war is influenced by factors such as the level of constraints against intervention on leaders in neighboring states, the number of ethnic groups spanning national boundaries, and the amount of inter-regional trade between states. None of these more indirect forms of intervention have been included in any of the studies listed above.

  2. The effects of economic intervention. One important shortcoming of existing studies of intervention is that they have rarely systematically considered forms of involvement short of direct military intervention by other states, although material and logistical support to the antagonists often can be critical to war outcomes and the strategies parties choose. For example it seems highly unlikely that the rebels in Zaire could have toppled President Mobutu without support from Uganda and Rwanda, but neither of these states formally intervened in the conflict (McNulty 1999). The is an increasing literature in economics on foreign aid and economic growth, and foreign aid and conflict, but this relationship remains under-explored in the political science literature. Additionally, we know that one of the main predictors of civil war outbreak is per capita income, yet we know little about the ways in which outside states and international organizations can effect this important variable.

  3. Expectations about future intervention. To date, we know very little about the effect of external intervention and civil war onset. The decision to initiate a war, however, is likely to be influenced by expectations about the possibility of external aid and assistance for each side. Insurgent groups, for example, almost certainly base their decision to rebel in part on expectations of support from outside players such as diaspora communities and other sympathetic states. Gartzke and Gleditsch (2003) and Salehyan and Walter (2004) have begun research on the role that threats of intervention may exert on conflict behavior, but additional attention needs to be paid to this important relationship. (Regarding interstate war see Werner 2000).

  1. Better, More Appropriate Data. Although many interpretations have been offered of different causal linkages that may underlie the observed empirical relationships discussed above, there have been few efforts to discriminate between and test hypotheses on the specific linkages that may or may not operate. In order to do this we need to better integrate statistical models with measures of the attributes of non-state actors and sub-state regions. Most analyses consider whether individual countries experience war or remain at peace at a particular period of time, and try to account for the onset, duration or resolution of civil war using country-level data. If we are to truly understand the various effects of external intervention on the players involved in civil wars we need to reorient our studies away from individual nation states in the aggregate as the main units of analysis toward the attributes of non-state actors and their linkages to other actors. The Uppsala conflict dataset, as well as Walter and Gledtisch (2004) are beginning to add information at this level.

I’ve run out of space and time, but this memo should give enough material for a lively discussion. The most obvious and superficial implication to be drawn from existing empirical studies is that policy makers in outside states who want to shorten civil wars should stay out of the fight while it’s being conducted, but should offer to enforce a negotiated peace once it is over. But this is only the tip of the iceberg…

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