With growing concerns about the safety of U.S. interests in Cuba, the battleship USS Maine was sent from Key West, Florida to Havana harbor at the end of January 1898. Three weeks later, on 15 February, a fierce explosion on board the ship killed 260 members of the crew. An investigation was immediately launched, but in the meantime the sensationalist New York Journal and New York World newspapers reported that the ship had been sunk by Spain.
Although President McKinley initially opposed going to war, the wider public demanded action. Eventually he requested permission from Congress to send troops to Cuba in an attempt to end the civil war. Passed by a vote of 311 to 6 in the House and 42 to 35 in the Senate, the Joint Resolution for Cuban independence was followed by an ultimatum to Spain to leave Cuba or else face American military intervention.
In response to the ultimatum Spain severed diplomatic relations with the United States and, on 21 April, declared war. A U.S. blockade of Cuba began the same day. Congress didn’t formally declare war until 25 April, although the declaration recognized that a state of war had existed since Spain’s declaration four days earlier.