U.S. President William McKinley signs a joint resolution to Congress for declaration of war against Spain, beginning the Spanish–American War.

William McKinley was the 25th president of the United States, serving from 1897 until his assassination in 1901. A member of the Republican Party, he led a realignment that made Republicans largely dominant in the industrial states and nationwide for decades. McKinley successfully led the U.S. in the Spanish–American War and oversaw a period of American expansionism, with the annexations of Hawaii, Puerto Rico, Guam, the Philippines, and American Samoa.

The Spanish–American War was fought between Spain and the United States in 1898. It began with the sinking of the USS Maine in Havana Harbor in Cuba, and resulted in the U.S. acquiring sovereignty over Puerto Rico, Guam, and the Philippines, and establishing a protectorate over Cuba. It represented U.S. intervention in the Cuban War of Independence and Philippine Revolution, with the latter later leading to the Philippine–American War. The Spanish–American War brought an end to almost four centuries of Spanish presence in the Americas, Asia, and the Pacific; the United States meanwhile not only became a major world power, but also gained several island possessions spanning the globe, which provoked rancorous debate over the wisdom of expansionism.

April 20 is the 110th day of the year in the Gregorian calendar; 255 days remain until the end of the year.