Answer:
The United States declared war against Spain after the sinking of the USS Maine in Havana Harbor in 1898.
In January 1898, the USS Maine, a U.S. battleship sent to Havana, Cuba as a show of force during a period of political unrest, exploded and sank, killing 260 American sailors. While the exact cause of the explosion was never conclusively determined, many Americans blamed Spain, which ruled Cuba as a colony at the time.
Public outrage over the incident, combined with longstanding tensions over Spanish rule in Cuba and other territories, led to the U.S. declaring war on Spain in April 1898. The resulting conflict, known as the Spanish-American War, lasted only a few months and resulted in a decisive U.S. victory.
As a result of the war, Spain was forced to cede control of several of its colonial possessions, including Cuba, Puerto Rico, Guam, and the Philippines, to the United States. The Spanish-American War marked a turning point in American foreign policy, as the U.S. emerged as a global power with territorial holdings in the Caribbean and Pacific regions.