Between 1877 and 1918, the United States rose as a major economic and military power. Justifications for overseas expansion emphasized access to global markets, the importance of sea power, and the need to police international misconduct and trade. These justifications shaped U.S. policy toward European powers in Latin America, and victory in the War of 1898 enabled the United States to take control of former Spanish colonies in the Caribbean and Pacific. Victory, however, also led to bloody conflict in the Philippines as the United States struggled to suppress Filipino resistance to American rule.

After 1899, the United States aggressively asserted its interests in Asia and Latin America. In China, the United States used the so-called Boxer Rebellion to make good its claim to an “open door” to Chinese markets. Later, President Theodore Roosevelt strengthened relations with Japan, and his successor, William Howard Taft, supported U.S. business interests in China. In the Caribbean, the United States constructed the Panama Canal and regularly exercised the right, claimed under the Roosevelt Corollary, to intervene in the affairs of states in the region. President Woodrow Wilson publicly disparaged the imperialism of his predecessors but repeatedly used the U.S. military to “police” Mexico.

At the outbreak of World War I, the United States asserted neutrality, but its economic ties to the Allies rapidly undercut that claim. In 1917, German submarine attacks drew the United States into the war on the side of Britain and France. Involvement in the war profoundly transformed the economy, politics, and society of the nation, resulting in an economic boom, mass migrations of workers to industrial centers, and the achievement of national voting rights. At the Paris Peace Conference, Wilson attempted to implement his Fourteen Points. However, the designs of the Allies in Europe undermined the Treaty of Versailles, while Republican resistance at home prevented ratification of the treaty. Although Wilson’s dream of a just international order failed, the United States had taken its place as a major world power.