The Spanish–American War was an armed conflict between Spain and the United States in 1898. Hostilities began in the aftermath of the internal explosion of USS Maine in Havana Harbor in Cuba, leading to U.S. intervention in the Cuban War of Independence. On April 21, 1898, the United States declared war against Spain. ... The reasons for war were many, but there were two immediate ones: America's support the ongoing struggle by Cubans and Filipinos against Spanish rule, and the mysterious explosion of the battleship U.S.S. Maine in Havana Harbor.