On July 18, 1936, Spanish military units rose up against the democratically elected Second Republic, precipitating a bloody civil war that would rage for three years. Considered essentially a dress rehearsal for World War II, it pitted the right-wing forces of General Francisco Franco, aided by Fascist Italy and Nazi Germany, against a Soviet-backed coalition of socialists, anarchists, communists, regional separatists and democrats. Explore some fascinating facts about this ideologically fraught conflict, which resulted in a decades-long Franco dictatorship.

The rebels expected to take control quickly.

A cadre of rebel army officers began plotting to overthrow the government as soon as a leftist coalition won Spanish elections in February 1936. Gaining the support of General Franco at the final hour, they called for a July 18 uprising in Spanish Morocco, followed by a general uprising a day later, that they envisioned as a rapid coup d’état. But although they captured Spanish Morocco and the conservative heartland with barely a struggle, the Republican government retained about two-thirds of Spain, including most major cities. As civil war subsequently erupted, Franco ferried his battle-hardened troops from Morocco to the mainland—using planes and boats provided by Benito Mussolini and Adolf Hitler—and began marching northward toward Madrid.

Franco benefited from the untimely deaths of his rivals.

Though a key contributor to the coup, Franco didn’t originate the plot and was never supposed to lead the country. However, the rebels’ purported first choice for head of state, General José Sanjurjo, died in a plane crash just days after the uprising began while returning from exile in Portugal. Around the same time, Republican forces took out several of Franco’s other potential rivals, including monarchist politician José Calvo Sotelo, fascist politician José Antonio Primo de Rivera, and generals Joaquín Fanjul and Manuel Goded. By October 1936, Franco had been named commander in chief of the armed forces and head of the rebel Nationalist government. His final near-equal, General Emilio Mola, the technical mastermind of the coup plot, then died in a June 1937 plane crash, leaving him firmly and solely in charge.

The Republicans suffered from severe infighting.

While the Nationalists largely united behind Franco, the various Republican factions were constantly at each other’s throats. Tensions came to a boiling point in May 1937, when a police raid on the anarchist-controlled central telephone exchange in Barcelona sparked days of street fighting that left hundreds dead. This so-called civil war within the civil war, which pitted anarchists and anti-Stalin Marxists against Soviet-backed communists and the regional government, resulted in the communists—and hence Moscow—increasing their control over the war effort. Anarchist and anti-Stalin Marxist organizations were suppressed, and the revolutionary egalitarian fervor that had once gripped Barcelona died out.

Both sides committed widespread atrocities.

From the very beginning, Franco’s Nationalist troops initiated a campaign of terror in which they killed, tortured and shamed perceived political opponents. In August 1936, for example, they gunned down up to 4,000 alleged Republicans in the town of Badajoz and then burned the bodies at a local cemetery. Similar massacres occurred in Málaga, Toledo and elsewhere, each time with the tacit approval of the rebellion’s top leaders, such as Mola, who declared at one point, “We have to create the impression of mastery, eliminating without scruples or hesitation all those who do not think as we do.” (Another Nationalist general was quoted saying, “I authorize you to kill like a dog anyone who dares oppose you.”) Though less systematic, Republicans committed their own share of atrocities, including the slaying of thousands of Catholic priests, monks and nuns, as well as a mass execution of alleged fascists just outside Madrid. In total, it’s estimated that the Nationalists murdered about 150,000 prisoners of war and civilians over the course of the conflict—plus another 20,000 following their victory—compared to about 49,000 murders at the hands of the Republicans.

Thousands of Americans signed up to fight.

Although the U.S. government stayed neutral in the Spanish Civil War, about 2,800 Americans—many of whom had never before fired a gun—volunteered for the Republican cause. A diverse bunch, their unit, the so-called Abraham Lincoln Battalion, included a vaudeville acrobat, a rabbi and the first African-American ever to lead white troops into battle. Morale quickly deteriorated, however, after they were forced into several ill-advised charges against entrenched opposition. “We are shock troops,” a wounded American reportedly said from his hospital bed. “The Republic had to push some meat out there in front, and we were elected.” By the time the Lincolns departed Spain in October 1938, more than a quarter of them had perished. The roughly 40,000 international volunteers from other countries didn’t fare much better, suffering casualties at a far greater rate than the Spanish members of the Republican army.

Texaco’s CEO personally assisted Franco.

No more than a handful of Americans fought with the Nationalists. But Franco did gain the vital support of Texaco chief executive Torkild Rieber, a Norwegian-born American who admired Hitler and allegedly preferred doing business with autocrats. From his office high atop New York City’s Chrysler Building, Rieber illegally sold the Nationalists discounted oil on credit and illegally transported the fuel in his company’s own tankers. His worldwide network of employees passed along the whereabouts of Republican-bound oil shipments, thereby leaving them open to attack. For these blatant violations of U.S. neutrality acts, Texaco (now part of Chevron Corp.) received only a small fine.

A cornucopia of famous writers and artists covered the conflict.

Despite the danger, writers flocked to Spain during the civil war, with some fighting on the front lines and others filing articles from such places as the Hotel Florida in Madrid, a famed literary hotspot. “The Little Prince” author Antoine de Saint-Exupéry even flew his own plane to report on the conflict, whereas George Orwell survived a bullet wound to the neck while serving with a Republican militia. The poet Federico García Lorca, meanwhile, was assassinated by a Nationalist death squad. Other well-known literary figures in Spain at that time included Ernest Hemingway, Pablo Neruda, John Dos Passos, Langston Hughes, Dorothy Parker, Lillian Hellman, André Malraux and Arthur Koestler. Artists likewise produced numerous memorable works about the war, most notably Pablo Picasso, whose painting “Guernica” depicts the bombing of a defenseless town by Hitler’s Condor Legion.