Brief and successful as it was, the “splendid little war” (in John Hay’s phrase) pointed up the need for a pair of overdue reforms in America’s military. In the course of overwhelming the Spanish defenders in Cuba, some American military units had fared much better than others. For example, during the climactic assault on San Juan Hill, as Lt. John J. Pershing (who would command America’s forces in World War I) recorded, “A converging fire from all the works within range opened upon us that was terrible in its effect; the 71st New York, which lay in a sunken road near the ford, became demoralized and wellnigh stampeded.” The New Yorkers were finally ordered to lie down in a thicket just to get them out of the way.

Part of the problem was the obsolete single-shot black-powder rifles the New York troops were using. Black powder was less powerful than modern smokeless powder, which virtually every European army (including the Spanish) had adopted by the 189Os. It also fouled gun barrels, and each shot created a cloud of smoke “somewhat the size of a cow,” in one private’s words, that revealed the shooter’s position while obscuring his target. Regular Army infantry had been equipped with repeating smokeless rifles for several years, and Theodore Roosevelt made sure that his men got them too. Other volunteer regiments, lacking the Rough Riders’ clout, had to make do with whatever could be scraped up.

The Spanish-American War brought home the inadequacy of this arrangement. The Army quickly eliminated black powder for both infantry and artillery. (It also, among other reforms, adopted lightweight uniforms for tropical use in place of its standard heavy woolens, which had been unbearably hot in the Cuban summer.) More fundamentally, America’s military thinking finally shook itself free from the Revolutionary-era ideal of a small standing army supplemented with independent state-trained reserves. A 1902 law put state National Guard units under federal control, ensuring that they would be well equipped and close to battleready when needed. The law also eliminated, at long last, the archaic (and widely ignored) requirement that all able-bodied men in a community enroll and muster for militia drill. In doing so, the government finally recognized that a citizen militia made up of farmers summoned from their fields, providing their own arms as envisioned in the Second Amendment, no longer made sense in the twentieth century.