"Anti-imperialism" in political science and international relations is a term used in a variety of contexts, usually by nationalist movements, who want to secede from a larger polity (usually in the form of an empire, but also in a multi-ethnic sovereign state) or as a specific theory opposed to capitalism in Marxist–Leninist discourse, derived from Vladimir Lenin's work Imperialism, the Highest Stage of Capitalism. A less common usage is by isolationists who oppose an interventionist foreign policy.
People who categorise themselves as anti-imperialists, often state that they are opposed to colonialism, colonial empire, hegemony, imperialism, and territorial expansion of a country beyond its established borders. The phrase gained a wide currency after the Second World War and at the onset of the Cold War as political movements in colonies of European powers promoted national sovereignty. Some "anti-imperialist" groups who opposed the United States supported the power of the Soviet Union, such as in Guevarism, while in Maoism, this was criticized as "social imperialism". In the Arab and Muslim world, the term is often used in the context of anti-Zionist nationalist and religious movements.
In the late 1870s, the term Imperialism was introduced to the English language by opponents of the aggressively imperial policies of British Prime Minister Benjamin Disraeli (1874–80). It was shortly appropriated by supporters of "imperialism" such as Joseph Chamberlain. For some, imperialism designated a policy of idealism and philanthropy; others alleged that it was characterized by political self-interest, and a growing number associated it with capitalist greed. John A. Hobson and Lenin added a more theoretical macroeconomic connotation to the term. Many theoreticians on the left have followed either or both in emphasizing the structural or systemic character of "imperialism." Such writers have expanded the time period associated with the term so that it now designates neither a policy, nor a short space of decades in the late 19th century, but a global system extending over a period of centuries, often going back to Christopher Columbus and, in some facts, to the Crusades. As the application of the term has expanded, its meaning has shifted along five distinct but often parallel axes: the moral, the economic, the systemic, the cultural, and the temporal. Those changes reflect—among other shifts in sensibility—a growing unease with the fact of power, specifically, Western power.