Political Realism has been described as the “oldest theory” of international politics, as well as the “dominant” one. Central to the realist tradition is the concept of “security.” Realism sees the insecurity of states as the main problem in international relations. It depicts the international system as a realm where “self-help” is the primary motivation; states must provide security for themselves because no other agency or actor can be counted on to do so. However, realists offer different explanations for why security is scarce, emphasizing a range of underlying mechanisms and causal factors such as man’s innate desire for power; conflicts of interest that arise between states possessing different resource endowments, economic systems, and political orders; and the “ordering principle” of international anarchy. They also propose numerous factors that can intensify or ameliorate the basic security problem, such as polarity, shifts in the overall balance of power, the “offense–defense balance,” and domestic politics. Several alternative approaches to international relations have challenged the basic realist account of the security problem, three of which are democratic peace theory, economic liberalism, and social constructivism. Furthermore, realism outlines various strategies that states can pursue in order to make themselves more secure, such as maximizing power, international alliances, arms racing, socialization and innovation, and institutions and diplomacy. Scholars continue to debate the historical roots, conceptual foundations, and predictive accuracy of realism. New avenues of research cover issues such as civil war, ethnic conflict, mass violence, September 11, and the Iraq War.