What effect do third parties have on the evolution of civil wars? The authors argue that intervention by third parties is central to the civil war process, a process that is characterized by the duration of hostilities and the type of outcome. The authors examine empirically the effect of third-party intervention into civil wars during the period 1816—1997, using the event history framework of competing risks. From the perspective of competing risks, as a civil war endures, it is at risk of experiencing a transition to one of three civil war outcomes in our sample: military victory by the government, military victory by the opposition group, and negotiated settlement. The competing risks approach provides considerably better leverage on the dynamic qualities of civil wars and, in particular, the influence of interventions by third parties. The analysis suggests that third-party interventions can be decisive in the evolution of civil wars and that third-party interventions have a different effect on the duration than different civil war outcomes. The results show that third-party intervention decreases the time until the supported group achieves military victory. Furthermore, third-party interventions, on both the government and opposition sides, increase the time until a negotiated settlement.

We introduce the conditional frailty model, an event history model that separates and accounts for both event dependence and heterogeneity in repeated events processes. Event dependence and heterogeneity create within-subject correlation in event times thereby violating the assumptions of standard event history models. Simulations show the advantage of the conditional frailty model. Specifically they demonstrate the model's ability to disentangle the sources of within-subject correlation as well as the gains in both efficiency and bias of the model when compared to the widely used alternatives, which often produce conflicting conclusions. Two substantive political science problems illustrate the usefulness and interpretation of the model: state policy adoption and terrorist attacks.

The opportunity and willingness framework has received much attention in research on interstate conflict expansion. This framework is extended here by examining when and what side third parties join during ongoing conflicts. It is maintained that without examining both timing and side selection, understanding of conflict expansion is limited. The timing and side joined in interstate disputes between 1816 and 2001 are analysed using a competing risks duration model. The findings contribute novel insights into many key debates in conflict research such as balancing versus bandwagoning, as well as alliance reliability and the democratic peace. The results also indicate that relying on statistical models that do not distinguish between which side a third party can join may produce misleading results.

A rich literature addresses how a state's capabilities, its desire to aid or exploit a warring neighbor, and its alliance commitments determine whether or not the state joins an ongoing conflict. However, an important geopolitical consideration -proximity to the location of the ongoing conflict -has yet to be examined. The authors argue that states are more likely to join conflicts that occur close to their territories than conflicts that are located at a greater distance, and that accounts that do not pay attention to this distance are incomplete. Proximity to the location of an ongoing conflict affects the opportunity for a state to join (by decreasing costs), while also affecting the state's willingness to join (by increasing the potential threat to the state's security). A series of statistical models provide evidence for the authors' claims: a state's opportunity to join and its willingness to aid or exploit a neighbor in conflict, or to fulfill its alliance commitments, are each conditioned by its proximity to the location of the conflict. This conditioning effect of dispute location is important because it helps account for cases that appear to contradict the expectations of existing arguments regarding capabilities, contiguity, and alliances -such as when weak, non-contiguous, and non-allied states join ongoing conflicts and strong, contiguous, and allied states do not join.

T he possibility that actors strategically condition their behavior on partially unobservable factors poses a grave challenge to causal inference, particularly if only some of the actors whose behavior we analyze are at risk of experiencing the outcome of interest. We present a crisis bargaining model that indicates that targets can generally prevent war by arming. We then create a simulated data set where the model is assumed to perfectly describe interactions for those states engaged in crisis bargaining, which we assume most pairs of states are not. We further assume researchers cannot observe which states are engaged in crisis bargaining, although observable variables might serve as proxies. We demonstrate that a naïve design would falsely (and unsurprisingly) indicate a positive relationship between arming and war. More importantly, we then evaluate the performance of matching, instrumental variables, and statistical backwards induction. The latter two show some promise, but matching fares poorly.