In “Decline and Devolution: The Sources of Strategy Military Retrenchment,” Kyle Haynes builds a theory of how states react to decline across different regions. Haynes makes two key arguments. First, declining states should begin to retrench earlier when they have access to compatible successor states, which are willing and able to uphold the regional order as the waning state withdraws. Second, declining states should retrench more rapidly in regions that are less important to their security. The gist of our remarks is that, though we have qualms about the nitty-gritty, the work clarifies the big picture and substantially improves the literature on a number of fronts. This is real progress...