Which comes first? Unpacking the relationship between peace agreements and peacekeeping missions

Why do combatants engaged in civil conflict sign peace agreements when they do? Does a commitment by the United Nations (UN) to send a peacekeeping mission increase the probability that combatants will sign an agreement? With regards to the relationship between peace agreements and UN peacekeeping missions, previous studies of civil war have taken one of two positions: (a) a peace agreement between combatants causes an increase in the probability that the UN will send a peacekeeping mission to the conflict; or (b) the UN's decision to send a peacekeeping mission to a conflict causes an increase in the probability that combatants will sign a peace agreement. I contend that the UN's decision to send peacekeepers to a conflict and the combatant's decision to sign a peace agreement occur simultaneously. To overcome the simultaneity, I exploit exogenous variation in the UN's willingness to send peacekeepers to conflicts in the mid-1990s, based on the experience of the UNOSOM II mission in Somalia, to identity the causal effects that UN peacekeeping has on the likelihood of combatants signing peace agreements. Not accounting for endogeneity, the data suggest that the UN's willingness to send peacekeepers increases the probability of a peace agreement. A recursive bivariate probit model using Black Hawk Down as an instrumental variable, however, indicates that the UN's willingness to send peacekeepers to a conflict does not increase the probability that combatants will sign an agreement. This finding suggests that combatants sign agreements for reasons related internally to the conflict, not pressure from the international community.