In July of 1936, a failed military coup plunged Spain into civil war. The conflict pitted the leftist Republican government against fascist-backed Nationalists led by General Francisco Franco. With Adolf Hitler and Benito Mussolini already in power in Germany and Italy, anti-fascists around the world feared that Spain would be the next to fall, threatening the future of European democracy.

When world powers like the United States and the United Kingdom refused to intervene in the Spanish Civil War, more than 35,000 anti-fascist volunteers poured into Spain from 52 countries to take up arms against the Nationalists. They included Jewish refugees from Nazi Germany, idealist intellectuals like a young George Orwell and communists committed to crushing an ideological enemy.

“The Spanish Civil War looked like it could be the moment when fascism was finally thrown back,” says Richard Baxell, an historian and author of Unlikely Warriors: The Extraordinary Story of the Britons Who Fought in the Spanish Civil War. “There was this feeling that perhaps people could go out armed with just a gun and political conviction and do their bit alongside the Spanish people to defeat fascism at last.”

The foreign volunteers who fought in the “International Brigades” of the Spanish Civil War hoped to stop the march of fascism in Europe to avoid a much larger war. It didn’t work out that way.

The Spanish Civil War broke out less than 20 years after the end of World War I, and most world leaders desperately wanted to avoid being drawn into another global conflict potentially costing millions of lives.

In the United States, President Franklin D. Roosevelt failed to convince Congress to support the Spanish Republic. Instead, lawmakers passed a series of Neutrality Acts that cemented America’s isolationist stance in the 1930s.

In Europe, leaders from the U.K. and France called for all European nations to sign a non-intervention pact vowing to stay out of the civil war in Spain. All told, 27 countries signed the neutrality agreement, including Germany, Italy and the USSR. Hitler and Mussolini quickly violated the pact by sending arms and soldiers to assist Franco, and the Soviets eventually sent supplies and military advisors to aid the Republic.

As Franco’s Nationalists marched toward the Spanish capital Madrid in August of 1936, it was clear that no allies were coming to the defense of the Spanish Republic. That’s when the first foreign volunteers began to arrive in significant numbers, to fight alongside the Republicans under attack in Madrid.

Volunteers came from Poland, France, Britain, Ireland, Germany, Latin America, Canada and dozens of other countries, organizing themselves into ad-hoc columns that spoke the same language. Women came, too, mainly volunteering as nurses in military hospitals. Baxell says that roughly 70 percent of the volunteers were communists, since the communist party at the time was the “loudest and biggest organization that was battling fascism.”

By the fall of 1936, the Communist International or “Comintern”—a Soviet-led association of international communist parties—actively recruited foreign fighters who were organized into International Brigades like the Garibaldi Brigade (Italy), the Commune de Paris (France) and the Abraham Lincoln Brigade (USA).

The International Brigades fought bravely to help repel the Nationalists from Madrid, including Jewish refugees from Nazi Germany, who often led the charge as “shock troops."

“They were astonishingly brave,” says Baxell. “They went to where the fight was hottest and did everything they could to hold their ground. Many had experienced what was going on in Germany and knew they couldn’t go home. Better to die in Spain than in Germany.”

More than 2,800 Americans, many who were members of the American Communist Party, crossed the Atlantic to volunteer as part of the Abraham Lincoln Brigade. Around a third of the volunteers were Jewish, spurred by a desire to combat the spread of anti-semitic fascist regimes in Europe.

One of them was Milton Wolff, a young communist from New York City who went on to serve as a commander of the Lincoln Brigade. When asked by a Congressional committee in 1939 why he joined the Spanish Civil War, Wolff testified, “I am Jewish, and knowing that as a Jew we are the first to suffer when fascism does come, I went to Spain to fight against it.”

At least 90 members of the Lincoln Brigade were Black Americans who saw fascist oppression in Europe as an extension of racial oppression experienced at home in the United States. Many of the Black volunteers were also communists drawn to the American Communist Party’s vow to stand up for workers of all races. Black Americans bristled at Mussolini’s invasion of Ethiopia and knew that Hitler’s twisted aryan ideology had no room for people of color.

Vaughn Love, a Black volunteer, later said that "we didn't know too much about the Spaniards, but we knew that they were fighting against fascism, and that fascism was the enemy of all Black aspirations."

Of the roughly 35,000 foreign volunteers who fought in the Spanish Civil War from 1936 to 1939, an estimated 5,000 to 6,000 were killed and thousands more were recorded as missing. They paid the ultimate sacrifice for their ideals, but in the end it wasn’t enough. Franco and the Nationalists, with help from Hitler and Mussolini, overpowered the Republicans, took Madrid and won the war.

While some historians view the International Brigades as naive idealists or expendable pawns for the communist regime in the USSR, Baxell sees the volunteers in a more positive light.

“At the time, they showed the Spanish Republic and people around the world that Spain was not fighting fascism alone,” says Baxell. “Given what was going on in the world, that was a powerful message.”

In her farewell address to what remained of the beleaguered International Brigades in 1938, the Spanish Republican leader Dolores Ibarruri, known as “La Pasionaria,” praised the foreign volunteers:

“Communists, Socialists, Anarchists, Republicans—men of different colors, differing ideology, antagonistic religions, yet all profoundly loving liberty and justice, they came and offered themselves to us unconditionally… You are history. You are legend. You are the heroic example of democracy's solidarity and universality.”