Although this new thinking rapidly gained ground during the 1890s, it took the shock of tangible events to bridge the gap between ideas and action. After a revolution in Hawaii, which American officials actively abetted, the proposed annexation of Hawaii in 1893 reawakened the debate over colonial expansion but was blocked by the transfer of the presidency from Benjamin Harrison to Grover Cleveland. It was rather the revolt that began in Cuba in 1895 that ultimately mobilized the emotions and ideas of the new expansionism. In 1898 the United States was drawn into a struggle between Cuba and Spain that had brought mass suffering and wholesale destruction to its very borders. An aggressive national pride, emotional partisanship in favor of the Cubans, and tangible damage to American trade and property—all worked to arouse the public and the press, while the dramatic destruction of the battleship Maine acted as a spark to these combustibles. Originally regarded by most Americans as a crusade to free Cuba, the Spanish-American War quickly took on an expansionist thrust. The retention of Puerto Rico, Spain's other Caribbean colony, was soon regarded as a necessary war reparation. Strategically the key to the Pacific, Hawaii was annexed during the war by a joint resolution of Congress. Even the cries to free Cuba gave way to protests that the Cubans needed a period of tutelage before essaying complete self-government.
It was the Philippine Islands, however, that most forcefully brought the imperialist issue to a head. Large, populous, alien, and distant, they neither fell within the traditional geographical scope of American expansionism nor seemed even remotely assimilable to the American federal system. In the United States there had been little thought of acquiring the Philippines before the Spanish-American War, but once war came, the U.S. armed forces attacked them because they represented valuable enemy territory that was highly vulnerable. The initial American victories quickly led to a national conviction that the United States now controlled the islands and was responsible for determining their destiny. Expansionists were quick to argue that the nation should not turn the Filipinos back to Spanish misrule, while to let them drift would invite an Anglo-German struggle for their control. On the other hand, American rule could bring enlightenment to the islands, and their proximity to China might aid American penetration of what was assumed to be one of the great world markets of the future.
Expansionism carried the day, and the peace treaty with Spain provided for American possession of Puerto Rico, the Philippines, and Guam. Hawaii had already been separately annexed, and Cuba was subjected to a three-year military occupation followed by a theoretically sovereign independence in 1902. In fact, however, Cuba became a self-governing protectorate of the United States, with the latter nation retaining important governmental controls and the right of military intervention at its discretion, under the terms of the Platt Amendment of 1901. In the Philippines, meanwhile, an armed independence movement revolted against American rule in 1899, and the ensuing three-year Filipino-American War introduced the Americans to the frustrations and mutual atrocities characteristic of antiguerrilla warfare. The public had expected the Filipinos to greet the advent of American rule with cheers and were disillusioned to meet with hostility instead. Critics questioned the utility of the new colony and the morality of subduing it by force. While U.S. forces finally succeeded in crushing all resistance, anti-imperialists made the most of the contradictions inherent in spreading enlightenment at the point of a bayonet. Colonial empire quickly lost its glamour in the United States, while less formal techniques of expansion gained easier acceptance from the relative success of the Cuban protectorate program. In the twentieth century, American imperialism would be characterized by the extension of influence or control rather than by the outright annexation of territory.