International relations (IR) are the interactions among sovereign states. The scientific study of those interactions is also referred to as international studies, international politics, or international affairs. In a broader sense, the study of IR, in addition to multilateral relations, concerns all activities among states—such as war, diplomacy, trade, and foreign policy—as well as relations with and among other international actors, such as intergovernmental organizations (IGOs), international nongovernmental organizations (INGOs), international legal bodies, and multinational corporations (MNCs). There are several schools of thought within IR, of which the most prominent are realism, liberalism, and constructivism.