Answer:
In early 1898, McKinley ordered the U.S.S. Maine into Havana harbor. The battleship was sent to protect American citizens and their property in Cuba. After the Maine's arrival, U.S. newspapers published a letter stolen from the Spanish ambassador to the United States, Enrique Dupuy de Lome. The letter was insulting toward President McKinley. Americans were enraged and anti-Spanish feelings intensified.
Days later, the Maine mysteriously exploded in Havana harbor, killing more than two hundred American sailors. The cause of the explosion could not be officially determined. Whatever the actual cause, the American public blamed Spain. Calls for war became louder under the slogan, "Remember the Maine."
Spain tried to avoid war by making an agreement with the United States over Cuba. The American public, however, demanded war. McKinley asked Congress for authority to use force.