Spanish American War

The war began after the American demand for Spain's peaceful resolution of the Cuban fight for independence was rejected, though strong expansionist sentiment in the United States motivated the government to target Spain's remaining overseas territories: Cuba, Puerto Rico, the Philippines, Guam and the Caroline Islands.

Riots in Havana by pro-Spanish "Voluntarios" gave the United States a reason to send in the warship USS Maine to indicate high national interest. Tension among the American people was raised because of the explosion of the USS Maine, and "YellowJournalism" that accused Spain of extensive atrocities, agitating American public opinion. The war ended after decisive naval victories for the United States in the Philippines and Cuba.

Only 109 days after the outbreak of war, the Treaty of Paris, which ended the conflict, gave the United States control, among other territories, of the former Spanish colonies of Puerto Rico, the Philippines and Guam.

http://en.wikipedia.org/wiki/Spanish-American_War