In 1867, the United States purchased Alaska from Russia for $7.2 million. At the time, people thought the purchase was foolish, but in 1880 gold was discovered in the new territory. Hawaii also became a United States territory in 1898 after American planters revolted and overthrew the queen. Both Alaska and Hawaii became states in 1959.

When the battleship USS Maine was destroyed, the United States declared war on Spain in April 1898. Admiral George Dewey led the American fleet to attack the Spanish colony of the Philippines. Theodore Roosevelt formed a group called the Rough Riders and went to battle in Cuba. In August 1898, the Spanish-American War ended. A peace treaty gave Cuba its independence, and the United States possession of Puerto Rico, Guam, and the Philippines. In 1946, the Philippines became independent. Today, Guam and Puerto Rico are still part of the United States.