Imperialism: A policy or ideology by which a nation extends its power by acquiring territory or establishing economic and political dominance over other nations.
Spanish-American War: A conflict in 1898 between Spain and the United States, the result of which led to American control over the former Spanish colonies of Puerto Rico, Guam, and the Philippines.
Isolationism: A policy of remaining apart from the affairs or interests of other groups, especially the political affairs of other countries. The Anti-Imperialist League was a manifestation of isolationist sentiments in America.