Photographic History of the Spanish American War, p. 36. On April 25, 1898 the United States declared war on Spain following the sinking of the Battleship Maine in Havana harbor on February 15, 1898. The war ended with the signing of the Treaty of Paris on December 10, 1898. As a result Spain lost its control over the remains of its overseas empire -- Cuba, Puerto Rico, the Philippines Islands, Guam, and other islands.