International Relations as an academic discipline is very broad in its scope. It encompasses a number of other disciplines and fields.
The core concepts of International Relations are International Organizations, International Law, Foreign Policy, International Conflict, International Economic Relations, Military Strategy, International/Regional Security, Strategic Studies, International Political Economy, Conflict/War, Peace Studies, Globalization, and International Regimes.
Moreover, various other areas and fields like State Sovereignty, Ecological Sustainability, Nuclear Proliferation, Nationalism, Economic Development, Terrorism, Organized Crime, Human Security, Foreign Interventionism, and Human Rights also fall under the scope of International Relations.
The scope of International Relations has expanded greatly in modern times. Initially, the scope of International Relations was limited to the study of diplomatic history. IR concentrated on the study of contemporary foreign affairs with a view to drawing certain lessons. With the passage of time, much emphasis was laid on the study of International Law; thus IR began to be studied within the framework of International Law.
The scope of International Relations further expanded with the establishment of the League of Nations after the First World War, and the study of international organizations and institutions was also included within the scope of International Relations.
After the Second World War, the scope of International Relations further expanded due to significant changes that took place; for example, the emergence of the USA and the USSR as the two superpowers; the entry of a large number of non-European states into the society of nations; the danger of thermo-nuclear war; increasing interdependence of states, and rising expectations of the people in the under-developed world, etc.
Thus, with new developments, greater emphasis began to be laid on the scientific study of International Relations, which led to the development of new methodologies and the introduction of new theories in the study of International Relations.
In its scope, thus, International Relations is concerned with every form of interaction between and amongst nations. Such sort of interactions can also take place between corporations and social groups. For example, the interactions between the member states of OPEC, and the International Human Rights Commission.