This article discusses some of international law's contributions to international security, focusing primarily on the United Nations Charter and related doctrines that emphasize the importance of national territorial sovereignty. I analyze the Charter system's promise and limitations in dealing with certain persistent international security problems, including the existence of noncompliant states, threatening non-state actors, and normative challenges to expansive conceptions of national territorial sovereignty. I report data indicating that the United Nations framework -initially designed primarily to prevent aggressive war - has largely failed to contain violent international crises or to grapple with increases in the prevalence and intensity of civil war. To assess the importance of dealing with internal civil conflict in addition to aggressive war, I estimate the average length and intensity of civil wars taking place during several periods in history. The length of an average civil war has increased from just over 20 months in the 1901-1950 period to about 60 months in the period from 1951-1992, and intensity (measured by the number of battle deaths per hundred thousand people in the population of the country in question) has increased from under 3 (in the 1901-1950 period) to over 6 (1951-1992). I then review theories supporting the claim that international law can contribute to security despite the continuing extent of global conflict and violence, and conclude by discussing strategies to reform the United Nations system and enhance international law's contributions to peace in light of those theories. In particular, I emphasize the importance of two issues that affect international law's contributions but have not received sufficient attention. The first is the need for more empirical analysis of when domestic political bargains become sensitive to international law. The second issue concerns how international law should structure the choice between imposing collective sanctions on the people of a nation-state and using targeted remedies even if they involve incursions into a nation's territorial sovereignty. To address both of these issues, international law scholars may have to further reexamine assumptions about national territorial sovereignty long identified with international law.