This concluding chapter summarizes the book's main claims and empirical findings, discussing the implications of these findings as well as directions for future research. At their heart, alliance treaties are about using military force. As such, war planning can be conceptualized as the core of alliance treaty negotiations. Equipped with this premise, the book argued that the key variable determining whether conditions are conducive to agreement is the compatibility of the participants' ideal war plans. These plans must be both operationally and strategically compatible. When war plan compatibility is low, the second key explanatory variable comes into play: the number of negotiation participants that have attractive outside options. The chapter then highlights how the arguments and evidence in the book indicate new research directions in four areas related to alliances: alliance treaty design, alliance reliability, NATO expansion, and the formation of defense cooperation agreements.
