Civil wars show a remarkable variation in how long they last. Some end within days; others continue for decades. What explains the extreme intractability of some wars while others are resolved quickly? This article argues that conflicts with multiple actors who must approve a settlement (veto players) are longer because there are fewer acceptable agreements, information asymmetries are more acute, and shifting alliances and incentives to hold out make negotiation more difficult. This veto player approach to explaining variation in civil war duration is tested using a new dataset containing monthly data on all parties to each civil war begun since World War II. The statistical analysis shows a strong correlation between the number of veto players and the duration of civil war.C ivil wars show a remarkable variation in how long they last. A survey of all civil wars begun in the last 60 years reveals that, while a quarter of the wars end within the first eight months, another 25% continue for longer than five years. Moreover, 8% of all civil wars last more than two decades. What explains this wide variation in the duration of civil wars? Why are some civil wars resolved quickly while others drag on for decades without resolution?Civil war duration is an important topic for two main reasons. Theoretically, understanding how and why civil wars are resolved through negotiated settlement inherently involves an analysis of why it takes so long for settlements to be reached. To understand what causes combatants to fight and what gets them to cooperate, we must understand the duration of these conflicts. Practically, the costs of war tend to be directly related to its duration. Data on battle deaths in civil war reveal that internal conflicts that are two years or shorter generate an average of 3,000 deaths while civil wars that are longer than two years result in an average of 44,000 deaths. 1 For each additional month of civil war, on average, an additional 189 people are killed. 2 David E. Cunningham is a Postdoctoral Fellow at the John M. Olin , and the anonymous reviewers at AJPS.

Many rebel organizations receive significant assistance from external governments, yet the reasons why some rebels attract foreign support while others do not is poorly understood+ We analyze factors determining external support for insurgent groups from a principal-agent perspective+ We focus on both the supply side, that is, when states are willing to support insurgent groups in other states, and the demand side, that is, when groups are willing to accept such support, with the conditions that this may entail+ We test our hypotheses using new disaggregated data on insurgent groups and foreign support+ Our results indicate that external rebel support is influenced by characteristics of the rebel group as well as linkages between rebel groups and actors in other countries+ More specifically, we find that external support is more likely for moderately strong groups where support is more likely to be offered and accepted, in the presence of transnational constituencies, international rivalries, and when the government receives foreign support+

This paper introduces the Non-State Actors in Armed Conflict Dataset (NSA), which contains detailed information on the state–rebel group dyads included in the Uppsala Conflict Data Project Dyadic Dataset. Existing quantitative studies generally focus on characteristics of countries and conflicts to examine the duration, severity, outcome and recurrence of civil wars, in ways that often ignore the actors in civil wars. The NSA data provides additional information on the organizations involved in conflict dynamics. We describe the structure of the NSA data and the variables included, provide descriptive statistics of the indicators, and discuss areas for future research on non-state actors to enhance our understanding of conflict processes.

What explains the effect of external intervention on the duration of civil war? The literature on intervention has made some progress in addressing this question, but it has been hindered by an assumption that states intervene in civil wars either to help one side win or to facilitate negotiations. Often, however, external states become involved in civil war to pursue an agenda which is separate from the goals of the internal combatants. When states intervene in this fashion, they make wars more difficult to resolve for two reasons. First, doing so introduces another actor that must approve any settlement to end the war. Second, external states generally have less incentive to negotiate than internal actors because they bear lower costs of fighting and they can anticipate gaining less benefit from negotiation than domestic insurgents. Through Cox regressions using data on the goals of all interventions in civil wars since World War II, this article shows that when states intervene with an independent agenda, they make wars substantially longer. The effect of independent interventions is much larger than that of external interventions generally, suggesting that the established finding that external interventions prolong civil war is driven by a subset of cases where states have intervened in conflicts to pursue independent goals.

Theories of conflict emphasize dyadic interaction, yet existing empirical studies of civil war focus largely on state attributes and pay little attention to non-state antagonists. We recast civil war in a dyadic perspective, and consider how non-state actor attributes and their relationship to the state influence conflict dynamics. We argue that strong rebels, which pose a military challenge to the government, are likely to lead to short wars and concessions. Conflicts where rebels seem weak can become prolonged if rebels can operate in the periphery so as to defy a government victory yet are not strong enough to extract concessions. Conflicts should be shorter when potential insurgents can rely on alternative political means to violence. We examine these hypotheses in a dyadic analysis of civil war duration and outcomes, using new data on non-state actors and conflict attributes, finding support for many of our conjectures.