As the 21st century unfolds, the dynamics of population growth, settlement patterns, and movement across borders are certain to have an effect on international security. Demographic shifts in political environments that are already tense as a result of territorial disputes, ethnic rivalries, ideological divides, or environmental stresses may provide just enough pressure to spark a violent conflict or perhaps even outright war. Demographic factors are thus worthy of analysis as potential contributors to armed conflict. The author lays out a general framework for looking at population developments through the prism of security issues, proffering some preliminary assessments as to which trends or factors might threaten U.S. interests around the world. Based on this analysis, there appear to be three broad areas of response: (1) A useful practice would be to create and place increased focus on demographically oriented indicators and warning measures. It will be important to understand how demographic pressures might be constraining the actions of key allies, increasing frictions between key regional powers, and/or laying the foundations for ethnic conflict. (2) Carefully targeted foreign aid may help some key friends and allies to better manage the effects of rapid population growth, allowing them to conserve resources and reform their political systems to take into account emerging demographic realities. (3) From the U.S. Army's standpoint, the most important consequence of demographic trends is the increasing urbanization of conflict. In the short term, training will be important to obtain improvements in military operations on urbanized terrain (MOUT) capabilities. Over the longer term, research in new technologies will improve the ability of U.S. ground forces to operate in urban areas, for example, advanced intelligence-gathering platforms, better personnel protection, and a new generation of nonlethal weapons.