This article introduces the Alliance Treaty Obligations and Provisions (ATOP) dataset. We begin by describing the rationale for collecting the ATOP data, its scope, and some general coding rules for the project. Then we offer some descriptive statistics for phase one of the dataset, which covers the years 1815-1944, and reveal some interesting trends in alliance politics. Finally, we replicate a study of alliance formation originally conducted by Lai and Reiter (2000) to demonstrate the effect the use of ATOP data may have on past inferences about alliance politics.

The proposition that domestic political vulnerability provides an incentive for leaders to engage in international conflict has been widely accepted because of appealing logic and anecdotal support. Although empirical studies of U.S. behavior during the cold war era have demonstrated some support for a relationship between domestic political vulnerability and aggressive international behavior, the generalizability of these tests should not be assumed. In fact, there is little empirical evidence in support of this relationship as a general pattern. This study assesses theories linking domestic political vulnerability to international disputes on a cross-national basis by examining the relationships between economic decline, the electroal cycle, and measures of aggressive international action for 18 advanced industrialized democracies during the period from 1952 to 1988. The authors find no consistent support for a relationship between constraining domestic political conditions and international behavior. Instead, fewer international demands are made on politically vulnerable leaders. Due to strategic interaction in the international system, just when a state leader might be most willing to act aggressively, he or she is likely to have the least opportunity to do so. Variance in the behavior of international rivals may explain the lack of an empirical relationship between domestic political conditions and foreign policy behavior.

Understanding the conditions under which state leaders are willing to honor alliance commitments in war will increase knowledge about the escalation and diffusion of conflict and about the propensity of states to fulfill agreements under anarchy. New data analysis provides evidence that alliance commitments are fulfilled about 75 percent of the time. But how can one understand the failure of alliance partners to act as promised in the remaining 25 percent of cases? Formal modelers have deduced that because of the costs associated with alliances, state leaders who form alliances are likely to fulfill them; those alliances that are formed should be fairly reliable. I argue, therefore, that one can best account for violations of alliance agreements either through an understanding of the factors that reduce the costs of violation or through changes that have occurred since the alliance was formed. Using detailed data on alliance commitments between 1816 and 1944, I find evidence commensurate with this argument. Changes in the power of states or in their policymaking processes are powerful predictors of the failure to honor past commitments; and nondemocratic states and major powers, sets of states that I argue suffer lower costs from reneging on agreements, are more likely to violate treaties.

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Scholars have long debated the effects of military alliances on the likelihood of war, and no clear support has emerged for the argument that alliances improve the prospects for peace through effective deterrence nor that they kindle the flames of war. In this study, I argue that alliance commitments affect the probability that a potential challenger will initiate a militarized interstate dispute because alliances provide information about the likelihood that others will intervene in a potential conflict. Yet, different agreements provide different information. Alliance commitments that would require allies to intervene on behalf of potential target states reduce the probability that a militarized dispute will emerge, but alliance commitments promising offensive support to a potential challenger and alliances that promise nonintervention by outside powers increase the likelihood that a challenger will initiate a crisis. As diplomats have long understood, the specific content of international agreements helps to determine their effects.