What motivated the united states to enter into a war with spain?

A Cuban rebellion in search of Independence that was strongly supported by the media and the public as well as other events that caused the Spanish-American War:
1. de Lome Letter - de Lome was a Spanish ambassador in US. Sent letter back to Spain saying McKinley was weak and wouldn't fight. It was intercepted by and published in the New York Journal.
2. Battleship Maine - the sinking of the U.S. battleship Maine in Havana harbor, with a loss of 260 men. Although Spanish complicity was not proved, U.S. public opinion was aroused by yellow journalism and people began demanding to go to war to get revenge.