ASK MOST AMERICANS about colonial America, and they’ll think of the era before 1776. But the history that follows is also colonial — this time with America as colonizer rather than colonized.

Immediately after independence, the infant United States launched its own territorial empire. Canada was pre-approved for admission into the union in the Articles of Confederation, the national government that preceded the federal Constitution ratified in 1788. The Louisiana Purchase of 1803 added the middle of the continent, opening the door to the westward expansion of slavery and the dispossession of Native American lands. By 1848, the United States had sliced off about a third of Mexico. Defeating Spain 50 years later, the United States claimed the bulk of its overseas colonies, among them the Philippines, Puerto Rico, Guam, and Cuba. More island acquisitions followed in the early 20th century.

In our own day, many of these later gains are called territories or possessions, reminders that the dreaded word colony slipped out of the national vocabulary in the early 20th century. Today Americans rule an empire without colonies — or at least this is the story we tell ourselves.

Clay Risen examines the origins of this national myth in The Crowded Hour, a swashbuckling tale of future US president Theodore Roosevelt, his Rough Riders, and their famous charge up San Juan Hill in Cuba on July 1, 1898. By the end of that year, Spain had ceded Cuba and much more to US control.

Conceding that the charge itself was insignificant as far as great American battles go, Risen sees 1898 as a national turning point. It was now, in that “crowded hour” (as Roosevelt called it) that Americans rebranded imperialism as the idealistic exportation of liberty and humanitarianism, with commercial power and political protection tagging along in their wake. This paved the way for the activist American foreign policy of the 20th century — the American Century, as Time publisher Henry Luce famously labeled it.

The American Century did not dawn without a struggle. Risen divides his cast into the old guard, “noble relics” such as President William McKinley. Allergic to standing armies and centralized government, they longed for the isolationism of the 19th century. Their defining event was the Civil War, the national bloodbath whose destructiveness now seemed all the more foolish as Gilded Age plutocrats eyed foreign markets.

Risen’s heroes, Roosevelt and his Riders, represent the nation’s “dynamic future.” Weaned on tales of the Indian Wars and the winning of the West, they mixed fashionable social Darwinism with a bare-knuckle masculinity to arrive at a new philosophy of activist American imperialism. Dissenting voices at home cried jingoism and racism, but the new brand of imperialism carried the day.

By 1898, the United States had pivoted onto a new path, “one cloaked in idealistic rhetoric, one that would eschew the formal trappings of territorial conquest in favor of commercial power, political protectorates, and above all humanitarian intervention.” As Risen concludes, this “rhetoric of American idealism and power would change the world to a greater extent than guns and money ever would.”

If this tale seems familiar, that’s because it is. We’ve known this much for half a century, when historians, dutifully cited by Risen, locked the pivot story into place. The centennial of the war, however, emboldened a new group of scholars to recast this familiar tale. They pushed for a transnational approach to the age of imperialism that would take into account Cuban and Spanish archives and attitudes. As historian Louis A. Pérez observed in his centennial-year The War of 1898, without these non-US perspectives we simply repeat American accounts until they become self-evident truths. Although Risen doesn’t entirely ignore Cuban and Spanish voices, here he unapologetically spins what he calls a “quintessentially American story.” Cuba and Cubans, Spain and the Spanish recede almost entirely from view; when we see them, it is through American eyes. We still seem to be in the American Century: the world is the stage, but the star of the show is the United States.

Still, The Crowded Hour is a good yarn. Risen’s special talent is the character sketch, and between Roosevelt and the Rough Riders he has a lot to work with. Their official name was the First United States Volunteer Cavalry, and Risen deftly charts their unlikely path from training in Texas (the better to acclimate the men for Cuba) to the hellish boat passage from Tampa, where they roasted and vomited in the ships’ holds, and finally to Cuba. He is the camera zooming in and out, now guiding us in the fog of war, now pointing out the larger meaning of the small thing. Readers who want to watch the Americans take the Hill can skip directly to the bravura account in chapter 11. “That morning around the campfires, as the mists rose above El Poso and the San Juan River plain below them, there was only this: this valley, this hill, this fight.”

At the center of the story stands Theodore Roosevelt. We expect him to be larger than life, even cartoonishly so. But here he also seems to stand for something about our own era. Roosevelt was “a great leader,” Risen tells us. He was decisive, loyal to his men, an ox for work. More than this, Roosevelt had ideas — even a “coherent philosophy.” He read a lot and thought a lot. He wrote books and essays. His Strenuous Life issued a Kipling-esque call for Americans and America to take up the white man’s burden. Roosevelt “embraced the notion of a country brought together by common values and a mission to bring those values to the world.”

Hatched in the study and tested on the battlefield, Roosevelt’s ideas were and are anathema to many. Even now we are fighting over his ideas as they are embodied in the TR equestrian statue guarding the American Museum of Natural History. But still they were ideas — and you can’t help but think Risen wants us to take notice of the particular importance of that fact. Ideas are formulated thoughts. They result from intentional mental activity: reading, pondering, discussing, and reflecting. Ideas are therefore fundamentally different from instantaneous emotional reactions and personal attacks. To disagree with an idea, you must first stop and then think.

The Crowded Hour reminds us that great leaders need ideas, perhaps even a coherent philosophy, to take the nation in a new direction.

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Caroline Winterer is Anthony P. Meier Family Professor in the Humanities and director of the Stanford Humanities Center. She specializes in American history of the pre-1900 period, especially the history of ideas, political theory, and the history of science. Her most recent book is American Enlightenments: Pursuing Happiness in the Age of Reason (Yale, 2016).