How did the Spanish-American War turn into a war of imperial expansion?

In 1895, Cuba began a struggle for independence from Spain. Due to sensationalized reports of Spain's tyranny over the island, Americans grew increasingly anxious to get involved. After riots in Havana, the U. S. Navy dispatched the U.S.S. Maine to Cuba in order to protect U.S. citizens and property. That ship exploded and sank, killing 260 crew members. Although the exact cause of the disaster was unconfirmed at first, Congress and the American public blamed Spain, and desire for war with Spain increased. Congress issued a resolution calling for Spain to withdraw from Cuba and authorizing President William McKinley to use force to drive the Spanish out. The resolution specifically renounced the annexation of Cuba as a reason for American involvement in the situation.
Spain declared war first, and America declared war on Spain the next day. The U.S. Navy quickly subdued the Spanish Navy in the Philippines, and Theodore Roosevelt and the "Rough Riders" fought on the ground in Cuba. Puerto Rico was another battleground. The war lasted only a few months, with the United States achieving a quick and resounding victory. The Treaty of Paris delineated the terms for peace. It awarded Guam, Puerto Rico, and the Philippines to the United States. The McKinley administration also used the war to justify the annexation of Hawaii, whose new government had been requesting annexation since 1893. Although the United States did not overtly enter the war with the intention of gaining colonies, that was the outcome. These outposts beyond American shores allowed the country to gain a greater role in international politics.
https://history.state.gov/milestones/1866-1898/spanish-american-war

https://www.history.com/this-day-in-history/the-maine-explodes

https://www.history.com/topics/early-20th-century-us/spanish-american-war