Geographic proximity and third-party joiners in militarized interstate disputes

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.