When and why do states agree to settle border disputes? Why do interstate rivalries begin and end? Rider & Owsiak address both questions, integrating research programs on border settlement and interstate rivalry within an overall bargaining framework. First, they argue that border settlement is particularly difficult when the disputed territory contains 'power endowments', such as strategic territory or resources. These endowments create a commitment problem, as a state gaining territory may use its new power to demand additional concessions. Thus, states are unwilling to cede territory containing power endowments. Second, continued disputes over territory with power endowments make interstate rivalries more likely. States continue the contest for power endowed territory but may be reluctant to fight a full-scale war. Finally, once borders are settled, rivalries become less intense and may eventually end, as the key point of contention has been removed. The authors provide a significant amount of statistical evidence to support this theory, although they admit that the statistical models are consistent with the theory rather than a definitive causal test. The theory makes intuitive sense, although it does not include any formal models to confirm the logic. In several areas, future research can extend and clarify the theory. For instance, how would the pre-settlement status quo impact the bargaining situation? Do rivalries emerge more or less spontaneously out of disputes over power endowments, or are they deliberately instigated by one of the actors? Future research can also extend the empirical evaluation, especially using case studies to confirm the theoretical story. Overall, the book provides a reasonable explanation linking unsettled borders and rivalry and a solid foundation for future research.