On Feb. 15, 1898, the USS Maine was sunk in Havana Harbor where it was temporarily stationed to provide support for Americans in the city during Cuba’s war for independence from Spain. A subsequent naval board of inquiry concluded that there was no US negligence in operating the ship and that it was “destroyed by the explosion of a submarine mine.” Although it did not say Spain did it, that was the logical conclusion. And William Randolph Hearst’s newspapers launched a campaign “Remember the Maine” that fueled U.S. citizens’ pressure for war against Spain. 
For various additional reasons, Americans in 1898 “flocked to the cause of ‘Cuba Libre,’ especially once fighting broke out on the island in 1895. The plight of the Cubans was particularly affecting: “Over the next three years, hundreds of thousands of civilians died, many in Spanish concentration camps, the existence of which spurred hundreds of Americans to join illegal filibuster missions to aid the rebels.”
On April 11, 1898, President William McKinley asked the Congress “to authorize and empower the President to take measures to secure a full and final termination of hostilities between the government of Spain and the people of Cuba, and to ensure in the island the establishment of a stable government, capable of maintaining order and observing its international obligations, ensuring peace and tranquillity and the security of its citizens as well as our own, and to use the military and naval forces of the United States as may be necessary for these purposes.” 
In making this request, McKinley “was moved above all by this humanitarian impulse.. . . [The] primary driver was the widely held belief that Spain was destroying Cuba. ‘A country nearly as large as England, with all the material conditions of opulent civilization, has been made a charnel house,” said John James Ingalls, a Kansas politician. The Spanish-American War was a ‘popular’ conflict in the literal sense.”
Nine days later (April 20, 1898) the Congress adopted a joint resolution for “the recognition of the independence of the people of Cuba, demanding that the government of Spain relinquish its authority and government in the Island of Cuba and withdraw its land and naval forces from Cuba and Cuban waters, and directing the President of the United States to use the land and naval forces of the United States to carry these resolutions into effect.” What became known as the Teller Amendment was proposed by Senator Henry M. Teller (Rep., CO) and adopted by the Congress. It disclaimed “any disposition of intention to exercise sovereignty, jurisdiction, or control over said island except for pacification thereof, and asserts its determination, when that is accomplished, to leave the government and control of the island to its people.”
Because there were practically no military-trained men ready to fight, “McKinley authorized three volunteer cavalry regiments (800 to 1,000 soldiers), to be drawn from the ranks of men whose skills and life experiences made them predisposed to martial pursuits: cowboys, policemen, even college athletes.”
“The most famous of the three regiments, and the only one sent to Cuba, was the First United States Volunteer Cavalry — which reporters soon nicknamed the Rough Riders. Thanks to the renown of Theodore Roosevelt, who in 1897 as Assistant Secretary of the Navy, had said, ““A rich nation which is slothful, timid or unwieldy is an easy prey for any people which still retains those most valuable of all qualities, the soldierly virtues.”’and who in 1898 left the Department of the Navy to become the Volunteer Calvary’s lieutenant colonel, the regiment was overwhelmed with applicants.”
“The Rough Riders landed in Cuba on June 22, 1898. By August, Spain was suing for peace. In the subsequent Treaty of Paris, Spain recognized Cuba’s independence and ceded Puerto Rico, Guam and the Philippines to the U.S.
“Above all, the Rough Riders became instant celebrities because they embodied the public’s newfound, idealistic militarism. ‘Whether Fifth Avenue millionaires or Western cowboys, they fought together and died together in Cuba for the great American principles of liberty, equality and humanity,’ an editorialist for The Philadelphia Inquirer wrote.”
From the U.S. perspective, Teddy Roosevelt and the Roughriders military success in Cuba became part of U.S. legend, and Clay Risen, a deputy Op-Ed editor of the New York Times has revisited that legend in a Times article and a book.
Risen claims that this “war, however brief, was in fact a defining moment in America’s emergence as a global power. It captured the imagination of millions and changed how everyday citizens saw their place in the world. No longer content to merely inspire freedom for the world’s oppressed, . . . [many U.S. citizens] decided they had a personal obligation to bring freedom to them.”
“Underlying [this and other 20th century U.S. wars] is the same broadly held, deeply committed missionary zeal that drove . . . the Rough Riders to war. Until Americans learn to balance their commitment to global justice with an awareness of the limits to military prowess, the country will continue to make these mistakes.”
Nevertheless, Risen asserts that this was was “a half-baked, poorly executed, unnecessary conflict that pushed an immature military power onto the world stage.”
 See U.S. Entry Into Cuba’s War of Independence and Establishment of Protectorate of Cuba, dwkcommentaries.com (April 23, 2017). Michael Beschloss in “Presidents of War” asserts that the naval board of inquiry was under implicit pressure to conclude that the Navy was not at fault, but that subsequent Navy studies concluded that the cause probably was not a Spanish mine. Indeed, in 1976, a team of American naval investigators concluded that the Maine explosion was likely caused by a fire that ignited its ammunition stocks, not by a Spanish mine or act of sabotage. (See Beschloss Discusses “Presidents of War at Westminster Town Hall Forum, dwkcommentaries.com (Nov. 15, 2018).
 Teller Amendment, Wikipedia.
 Risen, The Rough Riders’ Guide to World Domination, N,Y. Times (June 2, 2019); Risen, The Crowded Hour: Theodore Roosevelt, the Rough Riders, and Dawn of the American Century (Simon & Schuster, 2019): Millard, Book Review: Teddy Roosevelt and the Rough Riders, N.Y. Times Book Review (June 4, 2019); Teddy Roosevelt and the Rough Riders Involvement in Cuba’s War of Independence, dwkcommentaries.com (June 20, 2019).