Fighting to Be Friends: Third-Party Bargaining, Alliance Formation, and War

Alliance formation typically entails some risk of abandonment, wherein an ally may not honor its obligations in the future. When potential security partners’ preferences are misaligned, this risk looms large, discouraging mutually beneficial investment in an alliance. How can a prospective ally credibly reassure an uncertain patron that their preferences align, to mitigate abandonment risks and elicit a security commitment? We show formally that pre-alliance bargaining with third parties is one way to do so. When the patron holds abandonment concerns, the prospective ally can reassure the patron by making greater concessions to the patron’s existing allies, but more hard-line demands of its rivals. This finding implies that the prospect of an alliance can alternately promote conflict with a prospective patron’s enemies and forestall conflict with its friends. Indeed, we show that incentives for pre-alliance reassurance can result in war, even with perfect asset divisibility, no commitment problems, and complete information among the belligerents. The results are illustrated by China’s intervention in the Korean War and Australia’s post-World War II rapprochement with Japan, which were motivated largely to foster security cooperation with the Soviet Union and the United States, respectively.