The Spanish Empire had been crumbling for a century, and there was a ferocious debate within the US over whether America should become an imperial power to replace it. This centered on Cuba: pro-imperialists wanted to purchase or annex it from Spain (pre-1861, the plan was to turn it into a new slave state); anti-imperialists wanted to support Cuban independence. In 1898, Cuban activists launched a war of independence from Spain, and the US intervened on their side. When the war ended in Spanish defeat, US anti-imperialists blocked the US from annexing Cuba, but pro-imperialists succeeded in placing it under a quasi-imperialist sphere of influence, seizing three other Spanish possessions: Puerto Rico, Guam, and the massive Philippines.
Theodore Roosevelt resigned as Assistant Secretary of the Navy in 1898 and organized the Rough Riders, the 1st United States Volunteer Calvary, composed of a diverse group of cowboys, miners, law enforcement officials, and Native Americans.
T. R. the Rough Rider:
Hero of the Spanish American War
(The real Rough Riders)
The Happiness Cycle