International relations (IR) or international affairs (IA) — commonly also referred to as international studies (IS), global studies (GS), or global affairs (GA) — is the study of interconnectedness of politics, economics and law on a global level. Depending on the academic institution, it is either a field of political science, an interdisciplinary academic field similar to global studies, or an entirely independent academic discipline in which students take a variety of internationally focused courses in social science and humanities disciplines. In all cases, the field studies relationships between political entities (polities) such as sovereign states, inter-governmental organizations (IGOs), international non-governmental organizations (INGOs), other non-governmental organizations (NGOs), and multinational corporations (MNCs), and the wider world-systems produced by this interaction. International relations is an academic and a public policy field, and so can be positive and normative, because it analyses and formulates the foreign policy of a given state. As political activity, international relations dates from the time of the Greek historian Thucydides (c. 460–395 BC), and, in the early 20th century, became a discrete academic field (no. 5901 in the 4-digit UNESCO Nomenclature) within political science. In practice, international relations and international affairs forms a separate academic program or field from political science, and the courses taught therein are highly interdisciplinary.[2] For example, international relations draws from the fields of politics, economics, international law, communication studies, history, demography, geography, sociology, anthropology, criminology, psychology, and gender studies. The scope of international relations encompasses issues such as globalization, diplomatic relations, state sovereignty, international security, ecological sustainability, nuclear proliferation, nationalism, economic development, global finance, terrorism, and human rights.