Choosing Sides in Wars

We present a rational-choice theory of how decision makers choose sides, or neutrality, in ongoing wars. The theory focuses on each nation's expected utility from the war's possible outcomes, and on each nation's utility for its available strategies. Once the decision-making calculus is specified, the theory is tested against more than two thousand national decisions to remain neutral or to join an ongoing war on one side or the other. The theory proves to have considerable explanatory power, with the results of the data analysis indicating that the basic decision-making calculus used to choose sides in wars has not changed substantially during the past century and a half, although there have been some adjustments upwards and downwards in the relative importance of particular elements in the calculus.