What is the policy of extending control of a nation or empire known as?

The correct choice is Imperialism, which refers to the policy or practice of extending a nation's authority and control over other countries or territories, often through military conquest or by exerting economic and political dominance. This term underscores the idea of larger powers influencing or controlling weaker regions and is often associated with historical contexts such as European expansion in the 19th and early 20th centuries.

In the broader study of anthropology and history, imperialism is distinguished from colonialism, which specifically involves the settlement and governance of a foreign territory. While expansionism deals with the growth of a country's territory, it may not necessarily imply the control or domination associated with imperialism. Nationalism, on the other hand, relates to a sense of pride or identity within one's nation, which can influence whether a nation engages in such policies but does not describe the act of extending control itself. Understanding these distinctions is crucial in analyzing historical and contemporary global power dynamics.