The Spanish-American War was a conflict between the United States
and Spain that ended Spanish colonial rule in the Americas which  
resulted in U.S. acquisition of territories in the western Pacific and
Latin America. Spain declared war on the United States on April 24,
followed by a U.S. declaration of war on the 25th, which was made
retroactive to April 21, the day the blockade of Cuba had begun. 

Teddy Roosevelt charging up the San Juan Heights with the
Rough Riders.