Final answer:
McKinley's request to Congress to declare war on Spain, following Spain's refusal to grant Cuban independence, resulted in Congress authorizing military force and passing the Teller Amendment, which barred the U.S. from annexing Cuba after the war.
Step-by-step explanation:
When President William McKinley asked Congress to declare war on Spain, it was following Spain's refusal to declare Cuba's independence and end its reconcentration policies in Cuba. Despite making some concessions, Spain did not guarantee Cuban independence, leading McKinley to seek military intervention.
On April 19, 1898, Congress responded by recognizing Cuba's independence and authorizing the use of military force, passing the Teller Amendment which stipulated that the United States would not annex Cuba post-war, ensuring support from those concerned about American expansionism. The declaration of war by Congress led to the Spanish-American War, resulting in the loss of Spanish control over Cuba, Puerto Rico, and other territories in the region.