When and whom to join: The expansion of ongoing violent interstate conflicts

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.