Global conflicts over resources, territories, and ideologies renewed debates over the nation's values and its role in the world, while simultaneously propelling the United States into a dominant international military, political, cultural, and economic position.
I. Many Americans began to advocate overseas expansionism in the late 19th century, leading to new territorial ambitions and acquisitions in the Western Hemisphere and the Pacific.
- The perception in the 1890s that the western frontier was "closed," economic motives, competition with other European imperialist ventures of the time, and racial theories all furthered arguments that Americans were destined to expand their culture and norms to others, especially the nonwhite nations of the globe.
- The American victory in the Spanish-American War led to the U.S. acquisition of island territories, an expanded economic and military presence in the Caribbean and Latin America, engagement in a protracted insurrection in the Philippines, and increased involvement in Asia.
- Questions about America's role in the world generated considerable debate, prompting the development of a wide variety of views and arguments between imperialists and anti-imperialists and, later, interventionists and isolationists.
- dollar diplomacy, Mexican intervention
II. World War I and its aftermath intensified debates about the nation's role in the world and how best to achieve national security and pursue American interests.
- After initial neutrality in World War I the nation entered the conflict, departing from the U.S. foreign policy tradition of noninvolvement in European affairs in response to Woodrow Wilson's call for the defense of humanitarian and democratic principles.
- Although the American Expeditionary Force played a relatively limited role in the war, Wilson was heavily involved in postwar negotiations, resulting in the Treaty of Versailles and the League of Nations, both of which generated substantial debate within the United States.
- In the years following World War I, the United States pursued a unilateral foreign policy that used international investment, peace treaties, and select military intervention to promote a vision of international order, even while maintaining U.S. isolationism, which continued to the late 1930s.
- Washington Naval Conference, Stimson Doctrine, Neutrality Acts
III. The involvement of the United States in World War II, while opposed by most Americans prior to the attack on Pearl Harbor, vaulted the United States into global political and military prominence, and transformed both American society and the relationship between the United States and the rest of the world.
- The mass mobilization of American society to supply troops for the war effort and a workforce on the home front ended the Great Depression and provided opportunities for women and minorities to improve their socioeconomic positions.
- Wartime experiences, such as the internment of Japanese Americans, challenges to civil liberties, debates over race and segregation, and the decision to drop the atomic bomb raised questions about American values.
- The United States and its allies achieved victory over the Axis powers through a combination of factors, including allied political and military cooperation, industrial production, technological and scientific advances, and popular commitment to advancing democratic ideals.
- Atlantic Charter, development of sonar, Manhattan Project
- The dominant American role in the Allied victory and postwar peace settlements, combined with the war-ravaged condition of Asia and Europe, allowed the United States to emerge from the war as the most powerful nation on earth.