New York University students in the Lincoln battalion, in April, 1938. Photograph from AP

On the morning of February 27, 1937, which began cold and gray, a few hundred Americans waited to storm a hill southeast of Madrid, near the Jarama River. They were volunteer soldiers, drawn to Spain by a noble cause. Germany belonged to Hitler, and Italy to Mussolini, but there was still a chance that the Spanish Republic—governed by an unstable coalition of liberals, socialists, and anarchists—could fight off a cabal of right-wing generals who called themselves Nationalists. The previous year, the Nationalists had tried to take over the country, touching off a civil war. Leftist volunteers from around the world flocked to the Republican side, seeing the war as a struggle between tyranny and freedom that transcended national boundaries. The fight felt almost holy—“like the feeling you expected to have and did not have when you made your first communion,” Ernest Hemingway wrote, in “For Whom the Bell Tolls.” The Americans had been brought to Spain by Comintern, the worldwide Communist organization, but, to disguise their allegiance, the troops had been given an irreproachably non-Communist name: the Abraham Lincoln battalion.

Entrenched at the top of the hill, behind a shot-up olive grove, were Moorish troops, flown in from Spain’s protectorate in Morocco in planes furnished by Hitler and Mussolini. The Moors were known to be especially formidable. “It was terrifying to watch the uncanny ability of the Moorish infantry to exploit the slightest fold in the ground which could be used for cover, and to make themselves invisible,” a volunteer later recalled. “It is an art that only comes to a man after a lifetime spent with a rifle in his hand.”

Most of the Americans, meanwhile, had fired a rifle for the first time less than two weeks earlier. Some had arrived at the war zone only a day or two before, still wearing street clothes and Keds, and had never fired a gun at all. Like the various luminaries who visited the front—Langston Hughes, W. H. Auden, Dorothy Parker, and others—many of the volunteers had a literary bent. An American ambulance driver named James Neugass worried in his diary about joining the “here-to-be-revolted-by-the-horror-of-war, later-to-write-a-book” tradition. A British volunteer, passing through a field where soldiers had lightened their packs, marvelled at the books they had left behind: “the works of Nietzsche, and Spinoza, Spanish language textbooks, Rhys David’s ‘Early Buddhism’ and every kind of taste in poetry.”

The commander of the American battalion was Robert Hale Merriman, a lumberjack’s son from California who was a graduate student in economics. He was six feet two, and in photographs his round horn-rimmed glasses make him look a bit like the silent-movie star Harold Lloyd. In “Spain in Our Hearts” (Houghton Mifflin Harcourt), a vivid and level-headed new history of American participation in the Spanish Civil War, Adam Hochschild quotes a diary entry of Neugass’s that nicely captures Merriman’s charisma: “He has a way of infecting the entire brigade with his almost too boyish enthusiasm.”

Merriman’s superior officers assured him that his troops wouldn’t be facing the Moors alone; at 7 a.m., he could expect support from artillery, planes, tanks, cavalry, armored cars, and, on his right flank, a Spanish battalion. But everything went wrong. The artillery fire landed three hours late and in the wrong place. The soldiers in the Spanish battalion advanced fifteen metres but then retreated to their trenches. Neither tanks nor horses materialized. Two armored cars showed up but didn’t fight. There was no sign of the planes, and, when Merriman checked with headquarters about them, he was faulted for not having set out an aviation signal to direct the pilots’ fire. It was the first he had heard of such a signal, but he ordered his soldiers to stitch one together, out of underwear and shirts. Two soldiers carried it from the trenches and, since it was by then broad daylight, were killed by machine-gun fire as they laid it down. In a phone call just before noon, a short-tempered Yugoslav colonel told Merriman that the Spanish troops were far ahead, waiting for him. Merriman could see that they were still in their trenches. “Don’t contradict me!” the Yugoslav, who had higher rank, yelled. He ordered Merriman to attack “at all costs.” Hochschild glosses the implicit threat here: a commander who hesitated during an offensive in Córdoba two months earlier had been shot as a Fascist spy.

After three Republican planes flew by, more or less harmlessly—as much support as the troops would receive—Merriman felt that he had no choice but to obey. He stepped out of the trenches, signalling to his men to follow, and was shot in the left shoulder. His men advanced into what one later recalled as “an impenetrable steel wall” of bullets. Some sheltered for a while behind the thin olive trees. Hochschild reports that an estimated hundred and twenty men were killed and a hundred and seventy-five wounded. Snipers shot first-aid workers who were trying to fetch the fallen. In the afternoon, it began to rain, and the mud-coated corpses stranded in no man’s land took on “a curious ruffled look,” like dead birds, a survivor recalled. In 1967, when the historian Cecil D. Eby visited, he found a cairn of rocks, bones, skulls, and helmets that had been made by the Lincolns a few days after the fighting, when they burned their dead, who were too numerous to bury. The consensus among historians, including Hochschild, is that as a military operation the attack achieved nothing.

“You can say that the battalion was named after Abraham Lincoln because he, too, was assassinated,” a survivor told a reporter. Jarama was the first major engagement fought by Americans in the Spanish Civil War, and it turned out to be representative. Again and again, high-level commanders ordered Lincolns into attacks that officers in the field warned would be suicidal. The Lincolns’ sacrifices rarely won the Republic any tactical advantage, and, as Hochschild reports, foreign volunteers in Spain were “killed at nearly three times the rate of the rest of the Republican Army.”

Whereas Spain’s right united within a few months around a single leader—the cunning, ruthless Francisco Franco, who went on to rule as a dictator for three and a half decades—the left tore itself apart with squabbling and paranoia. Veterans came to feel that the idealism of the cause had been exploited, and many resented being policed by shadowy Communist enforcers. Not all were embittered by the experience, however. “We were naïve,” one American recalled, years later, “but it’s the kind of naïveté that the world needs.”

Until well into the twentieth century, Spain’s economy remained largely agricultural, and its great landowners were accustomed to a near-monopoly on political power, shored up by the authority of the Roman Catholic Church. This started to change quickly with the establishment of the Second Republic, in 1931. Parliament legalized divorce, cut government subsidies to the Church, and laid the groundwork for the redistribution of land. In February, 1936, after an alliance of centrist and leftist parties won a parliamentary election, peasants seized land, and mobs burned churches and stormed prisons, releasing political prisoners. A circle of generals, deciding that things had gone far enough, planned a coup d’état. It began on July 17, 1936, in Morocco, home of Spain’s army of Moors and foreign legionnaires.