On April 22, 1898, President William McKinley took a decisive step toward military engagement with Spain by calling for 125,000 volunteers to join the National Guard in the fight in Cuba. This call came just weeks after the U.S. public sentiment had turned sharply in favor of intervention in the Cuban struggle for independence against Spanish colonial rule. The popular outcry included an outpouring of support for the Cuban rebels, alongside media sensationalism exemplified by yellow journalism that depicted the Spanish as brutal and oppressive. Notably, the sinking of the USS Maine in Havana Harbor on February 15, 1898, had heightened tensions, leading many Americans to demand decisive action.

In conjunction with McKinley's call for volunteers, Congress acted swiftly to bolster the U.S. military capabilities by increasing regular Army forces more than twofold to 65,000 personnel. This expansion reflected the urgency for military readiness amid the escalating conflict with Spain, which had, until then, been considered a distant and relatively minor colonial rivalry for the United States. McKinley’s actions demonstrated a significant pivot from isolationism toward a more interventionist foreign policy framework. It was a clear indication that the U.S. was prepared to assert its influence in the Caribbean and beyond, signaling the country's emergence as a new global power.

The mobilization of volunteer troops took shape swiftly in response to McKinley's appeal. State governors began to prepare their militias and those eager for service flocked to enlistment offices. For many, this was a chance to demonstrate patriotism and engage in what was seen as a righteous cause. By May, volunteers were mustering throughout the country, excited by the prospect of battle and the romanticism of war, despite the grim realities ahead. The burgeoning American military presence would soon lead to the Spanish-American War, a conflict that would last only a few months but would fundamentally reshape the geopolitical landscape in the Americas and the Pacific.