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Research

Hulme, M Patrick, and Erik Gartzke. 2021. “The Tyranny of Distance: Assessing and Explaining the Apparent Decline in U.S. Military Performance.” International Studies Quarterly 65(2): 542–50. (link)

There is a growing sense that U.S. military effectiveness has been on the wane in recent years.  Is this the case? If so, what are the reasons for the decay in American combat performance?  We first examine the available systematic evidence for American military decline, showing that the United States has indeed experienced a drop in the quality of outcomes of its military contests. Observers have offered a number of explanations for declining American military success, most predominantly  an increase in intrastate conflict after the Second World War. After showing that a decline in performance is observed even after fully excluding intrastate conflict, we propose an alternative explanation: the increasing distance-from-home at which the United States has been fighting. Distance is tyrannical: it saps military strength and increases the cost of contests, even as it reduces U.S. expertise and motivations to prevail. We then show that the distance from home at which the United States fights is the best predictor of the outcome of the conflict. We conclude by noting some avenues for future research and policy implications as the world returns to great power competition.

Power, Parity and Proximity (with Erik Gartzke, Lauren Gilbert and Alex Baithwaite)
(Revise and Resubmit at
Journal of Conflict Resolution)

Research debating competing perspectives on power and war has yet to address the endogenous impact of proximity. If power declines in distance, then power relations between two nations differ at different points on the globe. Claims about the impact of parity or preponderance on conflict and peace then really only apply to particular points or regions in the space separating borders or national capitals. We use a formal bargaining model to demonstrate that dyads should be most prone to fight in places where each state’s capabilities, discounted by distance, are roughly at parity. We then assess this relationship empirically, introducing the directed dyad year location unit-of-analysis to capture the impact of geographic distance on power and the propensity to fight. Results confirm that disputes are most likely at locations where the distance-weighted capabilities of nations are roughly equal.

War and Responsibility: Executive Constraint Overlooked (Revise and Resubmit at American Political Science Review)

In the context of the war powers, it is widely believed that the United States has a little-constrained “imperial presidency”. Congress avoids going “on the record” on matters of war and peace, and American presidents de facto have virtually unlimited discretion over use of military force decisions. Overlooked, however, is that with great power comes great responsibility. American combat deaths in less-than-successful military ventures expose presidents to political costs more easily levied on an executive that acts absent sufficient political cover from lawmakers. Taking account of these Loss Responsibility Costs, this article shows that the United States actually has an executive substantially constrained by Congress.


A model of the war powers factoring in these costs in a crisis bargaining game is introduced, and two principal results are highlighted. First, while smaller uses of force are undertaken unilaterally, the largest uses of force (i.e., full scale wars) are only undertaken subject to formal authorization from Congress. Second, exposure to these costs constrains presidential behavior even in the context of smaller uses of force undertaken unilaterally. Empirical evidence supporting both propositions is then provided. Novel data gathering sentiment from congressional floor speeches in nearly two hundred crises shows that, far from having an imperial presidency, congressional sentiment appears to operate as a necessary condition in degree for the scale of force utilized by the White House.

The War Powers and the Search for Credibility

American politicians have for decades perceived a close link between coercive credibility and the question of the war powers of Congress and the President, and yet scholars of political science have given relatively little attention to the subject. This article develops a formal model of the war powers, with a focus on the effect of asymmetric information over a Presidency's willingness to act unilaterally: the institution's sensitivity to "loss responsibility costs". A key intuition shown is that the primary effect of formal authorization from the legislature  is not purely informational, as prior models of domestic politics seemingly suggest. Instead, formal authorization serves as a functional role as an "incentives-rearranging" type mechanism, making intervention---and intervention at a higher scale---much more likely. Moreover, a vote in favor of war can make war less likely by removing the source of this information asymmetry. 

At the same time, the model shows that the act of seeking authorization can expose the institution of the Presidency as a weak type; acting unilaterally serves as a costly signal of the Presidency's insensitivity to loss responsibility costs. Specifically, the scale of the potential use of force heavily determines which effect dominates. While Presidents benefit greatly from the political cover of formal authorization, they therefore resist appearing too eager for the backing of the legislature and will act unilaterally for smaller uses of force. Presidents are shown to have strong incentives to carefully cultivate and maintain an image of an "imperial presidency".

Mind the Gap: “Constitutional Processes”, Alliance Commitment, and the Imperial Presidency (with Matt Waxman)
(Under Review)

An overwhelming majority of Americans support U.S. alliances, but at the same time strongly dislike the idea of an imperial presidency able to use military force unilaterally. We argue these two positions exist in irreconcilable tension with one another. American alliances in their very terms contain a “commitment gap” between the level of commitment required to effectively reassure allies, and that actually contained in the treaty text. Specifically, while allies seek for the American commitment to be “automatic” in case of attack, each American defense arrangement is conditioned upon the United States’s “constitutional processes.” In a self-help world, allies are highly sensitive to this disparity, pressuring the executive branch to “bridge the gap” through means such as broad assertions of presidential power, demonstrative uses of force, and tripwire deployments. The article illustrates the logic of the theory through case studies of American alliances with NATO, South Korea, the Philippines, and Thailand. It concludes by considering implications for contemporary efforts to reform the war powers.

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