Is this a private fight or may anybody join? Unexpected events and the spread of interstate war, 1815--1995

This thesis analyzes the role that unexpected political and military events play in causing states to join ongoing interstate wars. It is posited that such events reveal information which in turn causes states to reconsider their decisions to remain non-belligerents and often cause states to join an ongoing war. It is also posited that unexpected events can cause states to reconsider remaining in a war, are often responsible for states exiting wars and ultimately war termination. These hypotheses are tested using a Generalized Estimating Equations on a dataset of all interstate wars from 1815-1995 and in cases on the Crimean War, Franco-Prussian War and First World War.