International relations is the study of interactions among nations—and sometimes non-nations, such as terrorist groups or multinational corporations—at a global level. It seeks to understand how states interact with one another in areas like peacemaking, trade and warfare. It also examines the formal diplomatic ties between countries and their informal networks that influence their international dynamics.
A central concept in the field is state sovereignty, which posits that countries—monarchs then, and governments now—control what happens within their borders. However, a country’s power to act in the world is limited by its national resources and the international community’s perception of its legitimacy as a sovereign state. This constraint has led to international organizations such as the UN and NATO, which establish collective security and free trade respectively. It has also given rise to concepts such as the Responsibility to Protect and liberal intervention, which posit that states can intervene in the internal affairs of other countries in cases of genocide or mass atrocity.
The most prominent theory in IR is realism, which argues that states are driven by the pursuit of power and their own self-interests, and that conflict is an inherent part of the international environment. By contrast, liberalism focuses on the role of international institutions and the need for cooperation between states to prevent war and promote peace.
Various other theories exist as well, such as institutionalism, which draws upon game theory to explain how cooperation arises in an environment of anarchy, and Marxism, which sees the international system as a complex web of class struggle that generates social change at a global level. Other schools of thought in IR include feminist and post-colonialist approaches, which emphasize the important role played by gender, race, culture and history in international politics.