Final answer:
The explosion of the USS Maine in Havana Harbor was the primary event that led the United States to declare war on Spain and begin the Spanish-American War in 1898. Public outcry and the slogan "Remember the Maine" galvanized support for the war, which ended with Spain ceding several territories to the U.S. and acknowledging Cuban independence.
Step-by-step explanation:
The explosion of the USS Maine in Havana Harbor on February 15, 1898, was the catalyst that finally pushed the United States to enter into conflict with Spain, marking the start of the Spanish-American War. The battleship had been dispatched to Cuba to protect American interests during the Cuban revolt against Spanish rule. When the Maine sunk, resulting in the loss of 266 lives, the American public, fueled by yellow journalism, was quick to blame Spain for the explosion. This incident intensified the call for American intervention and contributed to Congress declaring war on Spain on April 25, 1898, under the rallying cry "Remember the Maine!"
President William McKinley had initially sought to avoid war, making a final attempt at peace by demanding Spain end its repressive policies in Cuba and declare Cuban independence. Spain's refusal left the U.S. little choice but to support the cause for Cuban liberty. The onset of the war led to significant naval battles and ultimately resulted in the defeat of the Spanish forces. As a result of the war, by the end of 1898, Spain acknowledged Cuban independence and ceded control of Guam, Puerto Rico, and the Philippines to the United States, thereby ending its role as a colonial power and marking the beginning of the U.S.'s emergence as an imperial power.