Civil wars vary greatly in duration—some end within months; others last for decades. What explains this variation? Civil wars drag on when no combatant can win a military victory and the various actors involved are unable, or unwilling, to reach a compromise agreement that resolves the war. Military victory does happen in civil war, but it is rare, so understanding why civil wars last as long as they do requires examining the barriers to negotiated settlement.
Wars last longer when the parties involved perceive the war as less costly relative to peace and when the combatants are overly optimistic about how they will do in the war. Even when key decision-makers see the war as costly and are realistic about their chances of prevailing, negotiated settlements prove elusive if the parties cannot accept a division of the issues at stake or if the government or rebels are unable to trust the commitments the other side makes in a negotiation. Additionally, bargaining is more complicated when there are more combatants that must accept the terms of any agreement, and conflicts with more combatants last much longer than those with fewer.
Many factors affect the bargaining environment, and these barriers to bargaining can explain why civil wars are on average quite long. International actions can alleviate some of the barriers and help combatants reach comprehensive settlements, as happened in the conflicts in Mozambique, El Salvador, Guatemala. In particular, peacekeeping and mediation strategies are effective at resolving wars sooner. International action in general is more effective, however, when the parties involved are interested in peace but need some help overcoming commitment or informational problems. These actions are much less successful when that interest is lacking.
The current civil war in Syria has many of the factors identified as prolonging wars. It is an extremely fractionalized conflict, and many external actors are involved. Syria has a large majority population that has been historically excluded from political power and economically marginalized, and a minority government that has been dominant. These factors make reaching a comprehensive settlement very challenging and mean the war is likely to be very long-lasting.