Various developments provoked the previously isolated United States to turn its attention overseas in the 1890s. Among the stimuli for the new imperialism were the desire for new economic markets, the sensationalistic appeals of the yellow press, missionary fervor, Darwinist ideology, great-power rivalry, and naval competition.

Strong American intervention in the Venezuelan boundary dispute of 1895 - 1896 demonstrated an aggressive new assertion of the Monroe Doctrine and led to a new British willingness to accept American domination in the Western Hemisphere. Longtime American involvement in Hawaii climaxed in 1893 in a revolution against native rule by white American planters. President Cleveland temporarily refused to annex the islands, but the question of incorporating Hawaii into the United States triggered the first full-fledged imperialistic debate in American history.

The splendid little Spanish-American War began in 1898 over American outrage about Spanish oppression of Cuba. American support for the Cuban rebellion had been whipped up into intense popular fervor by the yellow press. After the mysterious Maine explosion in February 1898, this public passion pushed a reluctant President McKinley into war, even though Spain was ready to concede on the major issues.

An astounding first development of the war was Admiral Deweys naval victory in May 1898 in the rich Spanish islands of the Philippines in East Asia. Then in August, American troops, assisted by Filipino rebels, captured the Philippine city of Manila in another dramatic victory. Despite mass confusion, American forces also easily and quickly overwhelmed the Spanish in Cuba and Puerto Rico.

After a long and bitter national debate over the wisdom and justice of American imperialism, which ended in a narrow proimperialist victory in the Senate, the United States took over the Philippines and Puerto Rico as colonial possessions. Regardless of serious doubts about imperialism, the United States had strongly asserted itself as a proud new international power.

Americas decision to take the Philippines aroused violent resistance from the Filipinos, who had expected independence. The brutal war that ensued was longer and costlier than the Spanish-American conflict.

Imperialistic competition in China deepened American involvement in Asia. Hays Open Door policy helped prevent the great powers from dismembering China. The United States joined the international expedition to suppress the Boxer Rebellion.

Theodore Roosevelt brought a new energy and assertiveness to American foreign policy. When his plans to build a canal in Panama were frustrated by the Colombian Senate, he helped promote a Panamanian independence movement that enabled the canal to be built. He also altered the Monroe Doctrine by adding a Roosevelt Corollary that declared an American right to intervene in South America.

Roosevelt negotiated an end to the Russo-Japanese War but angered both parties in the process. Several incidents showed that the United States and Japan were now competitors in East Asia.