Final answer:
President McKinley asked Congress to declare war on Spain because of the clear need to obtain justice for Cuban independence and due to Spain's refusal to grant such independence. Public pressure and the USS Maine incident influenced the decision, and the Teller Amendment was passed to assure non-annexation of Cuba. Therefore, the correct option is C.
Step-by-step explanation:
President McKinley asked Congress to declare war on Spain mainly because justice for obtaining Cuban independence was clear. He made one final effort to avoid war, but when Spain refused to end its reconcentration policy in Cuba and declare Cuba's independence, McKinley saw little choice but to act. The explosion of the USS Maine and public pressure after sensationalist news coverage also influenced his decision.
Public demand for intervention, based on humanitarian concerns and sensational journalism, pushed the government towards war. Ultimately, on April 19, 1898, Congress recognized Cuban independence and authorized the use of military force to remove Spain from Cuba while passing the Teller Amendment, which assured that the United States wouldn't annex Cuba after the conflict.