Since neither Spain nor the independence fighters could bring about a military decision in Cuba, the powerful neighboring state to the north took advantage of the situation to intervene.
In addition, the Asian market had long seemed enticing to the United States as well. The Philippines were of high strategic value, as Manila had become a hub of trade between East Asia and Latin America under the Spanish. The US had already shown clear interest in the Pacific islands of Hawaii (Hawaiian Territory) and Samoa. While interests in the Pacific were not sufficient to persuade the U.S. government to launch a war of aggression against Spain, the conquest of Manila was already part of the U.S. government's war scenarios that had been played out since 1896.
The majority of the US population sympathized with the insurgents in Cuba. The rebellion against a representative of the old world was compared in the press to the US struggle for independence. In contrast, the Spanish-Cuban colonial administration was using force against insurgents, a point emphasized in the U.S. press. Attitudes were more mixed on the question of whether the U.S. should intervene militarily. The Knights of Labor and American Federation of Labor (AFL) unions, for example, supported the uprisings in Cuba. A resolution for U.S. intervention, however, initially suffered defeat within the AFL because of fears of permanent U.S. expansion (replacing Spanish colonialism). Through euphoric media coverage, however, a clearly visible majority developed in favor of a declaration of war, which only the Socialists now opposed by a majority.
President Grover Cleveland stated in December 1896 that the United States would not show indefinite patience toward Spain, and President William McKinley finally elaborated in his Annual Message of 1897 that the United States might be compelled to intervene militarily in view of the continuing Spanish campaign of destruction. In March 1898, several politicians and advisors, including Henry Cabot Lodge, Sr. informed President McKinley that numerous U.S. businessmen were pressing for a quick resolution of the Cuban question due to economic losses. On March 27, 1898, McKinley issued an ultimatum to Spain demanding an armistice.
Against Spanish protests, the U.S. sent a battleship, the USSMaine under Captain Charles Dwight Sigsbee, on a "friendly visit" to Havana Harbor, arriving on January 25, 1898. At the same time, the U.S. fleet was massed at Key West, and preparations were underway for a blockade of the island to cut off Spanish troops from supplies and prevent further reinforcements.
To avoid being branded an aggressor, the Maine's commander forbade the crew to go ashore. However, on February 15, 1898, a devastating explosion occurred on his ship, killing 268 American sailors and soldiers. The United States accused Spain of perpetrating an attack; the American public was expectedly outraged. Publicists William Randolph Hearst and Joseph Pulitzer, among others, stoked sentiment against Spain. The battle cry of the Hearst press was Remember the Maine, to hell with Spain! ("Remember the Maine! To hell with Spain!"), a cause for war had been found. Hearst instructed his correspondent Remington to stay in Havana and supply pictures so that he, Hearst, could supply the war: "You furnish the pictures. I'll furnish the war."
The wreck of the USS Maine has become the subject of much research. Among other things, an investigation in 1976 came to the conclusion that a mine had not detonated under the ship, as claimed by the US government at the time, but that the explosion took place inside the USS Maine. It is possible that an undetected smouldering fire in one of the coal bunkers, which spread to a neighbouring magazine, could have caused the catastrophe (see also coal fire). A recent investigation, in the form of a simulation, by National Geographic Magazine (1999) does not rule out an externally caused mine explosion, without having sufficient evidence to support this hypothesis.
President McKinley, who had initially been opposed to war, under public pressure asked Congress for permission on April 11, 1898, to send troops to Cuba to take action against the Spanish. Mention of the independence question and of rebels as belligerents was cleverly avoided in the request. On April 19, the House and Senate jointly passed a Joint Resolution calling on Spain to withdraw from Cuba and authorizing President McKinley to use whatever military means were necessary to secure Cuba's independence from Spain. The Teller Amendment, named after Senator Henry M. Teller (Colorado), supplemented the resolution with the condition that the United States not annex Cuba after its independence was gained. This amendment was well received by the Cuban rebels and, despite concerns previously expressed by some rebels that the U.S. government might want to replace Spain's kingdom as colonial master, resulted in U.S. troops being welcomed by the rebels. The decision to interfere in the internal affairs of Spanish Cuba by military means was conveyed to Spain on April 20. Spain then broke off all diplomatic relations with the U.S. and in turn declared war against the U.S. on April 23.