Monroe Doctrine, Manifest Destiny, and "city upon a hill"
Monroe Doctrine--stated in 1820 that the Western Hemisphere was no longer open for colonization and the US would defend any place seeking independence. Cuba wanted independence from Spain.
Manifest Destiny--the US believed they were sanctioned by God to conquer land. Cuba had been on the radar since the 1840s and this war could give the US a chance to gain access to Cuba as well as gain land in the Pacific needed for naval build up.
"City upon a hill"--this phrase coming out of Massachusetts Bay Colony and owned by the US as a phrase claiming the US was a beacon of democracy. US imperialism was economic but also had a mission of spreading democracy to the world.