A recent article about the 1898 U.S. intervention in Cuba’s war of independence from Spain, asserts that at the time Americans “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.”
One of the supporters of this cause was Theodore Roosevelt, who as Assistant Secretary of the Navy in 1897 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.”
When President William McKinley declared war against Spain in April 1898, “he 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.
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, 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 Roosevelt, who left the Department of the Navy to become its lieutenant colonel, the regiment was overwhelmed with applicants.”
“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, “The Rough Riders landed in Cuba on June 22, 1898; by August, Spain was suing for peace.” In the subsequent peace treaty the U.S. acquired Puerto Rico, Guam and the Philippines and (until 1934) a de facto protectorate of Cuba. 
The author, Clay 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.”
Risen, The Rough Riders’ Guide to World Domination, N.Y. Times (June 2, 2019). This article is based upon the author’s forthcoming book on the Rough Riders: 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.
 See U.S. Entry Into Cuban War of Independence and Establishment of Protectorate of Cuba, 1898-1934, dwkcommentaries.com (April 23, 2017). According to historian Michael Beschloss, this U.S. intervention was started on the false premise that Spain had exploded the USS Maine in the Havana Harbor. (See Beschloss Discusses “Presidents of War” at Westminster Town Hall Forum, dwkcommentaries.com (Nov. 15, 2018).)