The United States and Spain quickly signed a preliminary peace agreement in which Spain agreed to liberate Cuba and cede Puerto Rico and Guam to the United States. But what would happen to the Philippines, an immense archipelago that lay more than 5,000 miles from California? Initially, the United States aimed to keep only Manila, because of its fine harbor. Manila was not defensible, however, without the whole island of Luzon, on which it sat. After deliberating, McKinley found a justification for annexing all of the Philippines. He decided that “we could not leave [the Filipinos] to themselves — they were unfit for self-rule.”

This declaration provoked heated debate. Under the Constitution, as Republican senator George F. Hoar argued, “no power is given to the Federal Government to acquire territory to be held and governed permanently as colonies” or “to conquer alien people and hold them in subjugation.” Leading citizens and peace advocates, including Jane Addams and Mark Twain, enlisted in the anti-imperialist cause. Steel king Andrew Carnegie offered $20 million to purchase Philippine independence. Labor leader Samuel Gompers warned union members about the threat of competition from low-wage Filipino immigrants. Anti-imperialists, however, were a diverse lot. Some argued that Filipinos were perfectly capable of self-rule; others warned about the dangers of annexing eight million Filipinos of an “inferior race.” “No matter whether they are fit to govern themselves or not,” declared a Missouri congressman, “they are not fit to govern us.”

Beginning in late 1898, anti-imperialist leagues sprang up around the country, but they never sparked a mass movement. On the contrary, McKinley’s “splendid little war” proved immensely popular. Confronted with that reality, Democrats waffled. Their standard-bearer, William Jennings Bryan, decided not to stake Democrats’ future on opposition to a policy that he believed to be irreversible. He threw his party into turmoil by declaring last-minute support for McKinley’s proposed treaty. Having met military defeat, Spanish representatives had little choice. In the Treaty of Paris, Spain ceded the Philippines to the United States for $20 million.

Annexation was not as simple as U.S. policymakers had expected. On February 4, 1899, two days before the Senate ratified the treaty, fighting broke out between American and Filipino patrols on the edge of Manila. Confronted by annexation, rebel leader Emilio Aguinaldo asserted his nation’s independence and turned his guns on occupying American forces. Though Aguinaldo found it difficult to organize a mass-based resistance movement, the ensuing conflict between Filipino nationalists and U.S. troops far exceeded in length and ferocity the war just concluded with Spain. Fighting tenacious guerrillas, the U.S. Army resorted to the same tactics Spain had employed in Cuba: burning crops and villages and rounding up civilians. Atrocities became commonplace on both sides. In three years of warfare, 4,200 Americans and an estimated 200,000 Filipinos died; many of the latter were dislocated civilians, particularly children, who succumbed to malnutrition and disease.

McKinley’s convincing victory over William Jennings Bryan in 1900 suggested popular satisfaction with America’s overseas adventures, even in the face of dogged Filipino resistance to U.S. rule. The fighting ended in 1902, and William Howard Taft, appointed as governor-general of the Philippines, sought to make the territory a model of roadbuilding and sanitary engineering. Yet misgivings lingered as Americans confronted the brutality of the war. Philosopher William James noted that the United States had destroyed “these islanders by the thousands, their villages and cities. …Could there be any more damning indictment of that whole bloated ideal termed ‘modern civilization’?” (American Voices).

Constitutional issues also remained unresolved. The treaty, while guaranteeing freedom of religion to inhabitants of ceded Spanish territories, withheld any promise of citizenship. It was up to Congress to decide Filipinos’ “civil rights and political status.” In 1901, the Supreme Court upheld this provision in a set of decisions known as the Insular Cases. The Constitution, declared the Court, did not automatically extend citizenship to people in acquired territories; Congress could decide. Puerto Rico, Guam, and the Philippines were thus marked as colonies, not future states.

The next year, as a condition for withdrawing from Cuba, the United States forced the newly independent island to accept a proviso in its constitution called the Platt Amendment (1902). This blocked Cuba from making a treaty with any country except the United States and gave the United States the right to intervene in Cuban affairs if it saw fit. Cuba also granted the United States a lease on Guantánamo Bay (still in effect), where the U.S. Navy built a large base. Cubans’ hard-fought independence was limited; so was that of Filipinos. Eventually, the Jones Act of 1916 committed the United States to Philippine independence but set no date. (The Philippines at last achieved independence in 1946.) Though the war’s carnage had rubbed off some of the moralizing gloss, America’s global aspirations remained intact.