is nation's policy of extending it's authority over other countries by political, economic or military means

Imperialism

Explanation:

Imperialism aims to create an "empire" of sorts, whereby a nation exercises authority or control over other countries in other parts of the world. Imperialism was pursued by European nations and by the United States in the late 19th and early 20th centuries. Gaining control or influence over territories, particularly in Africa and Asia, was seen as important to a nation's power and prestige. The most prominent example of US imperialism was the role the United States played in the Philippines.