Spanish-American War begins

On April 25, 1898, Congress declared that a state of war with Spain had existed since April 21, 1898, after President William McKinley asked for authority to intervene in Cuba. The declaration followed the explosion of the battleship USS Maine in Havana Harbor on February 15, 1898 and months of political pressure over Spain's war against Cuban insurgents. McKinley, Congress, and the United States Navy thus turned a crisis over Cuba into a formal war against Spain in the Caribbean and Pacific.

The declaration intensified the debate over whether the United States would act mainly as a protector of Cuban independence or as an emerging imperial power with overseas ambitions. Many members of Congress supported the Teller Amendment of April 20, 1898 to promise that the United States would not annex Cuba, while expansionists such as Theodore Roosevelt welcomed war as a chance to project American power abroad. The conflict also tested whether humanitarian rhetoric, commercial interests, and strategic naval thinking would combine into a new foreign-policy posture after the Civil War era.

The naval victory at Manila Bay on May 1, 1898 and the Army campaign in Cuba followed directly from the declaration of war. The Treaty of Paris signed on December 10, 1898 ended the war and transferred Puerto Rico, Guam, and the Philippines to the United States, making the Spanish-American War the opening act of a new American empire.