The figures of just how many volunteers there were are disputed , ranging from about 90 to 250.Given the nature that many American Blacks were not allowed in the US Military allied with the hazardous logistical barriers for the always harassed and harried US Communist Party of which many, though not all, were members made the journey nearly impossible.
The US contingent formed up as the Abraham Lincoln Brigade.
Compare and Contrast the attitudes and actions of Albert Einstein and Gene Kelly with General Motors ; Texaco and other Corporations in what Historian Paul Preston has rightly described as the actual beginning of WW2 in which Fascism tested the Worlds resolve and found ample grounds to be encouraged and emboldened.
The reaction of Western governments to the war was ambivalent and duplicitous. They agreed to a nonintervention pact and the United States embargoed aid to the Spanish belligerents, policies intended to de-escalate the war but whose selective enforcement undermined the Republic. While Germany and Italy supplied Franco with troops, tanks, submarines, and a modernized air force (the first to bomb open cities, most notably Guernica), the nonintervention policy only prevented arms from reaching the Republic. General Motors, Texaco, and other American corporations further assisted Franco with trucks and fuel. The Soviet Union and Mexico were the only governments to sell armaments to the Republic, although much of them were impounded at the French border. Throughout the war, a vociferous political and cultural movement in America rallied to the Republic by raising money for medical aid and demanding an end to the embargo. Such participants as Albert Einstein, Dorothy Parker, Gene Kelly, Paul Robeson, Helen Keller, A. Philip Randolph, and Gypsy Rose Lee reflected the wide base of support for the Republican cause.
You can find a synopsis of the trials and tribulations of the formation and continuation of the Abe Lincoln Brigade before they even got anywhere near Spanish Soil in this very informative concise piece.
The Lincolns came from all walks of life, all regions of the country, and included seamen, students, the unemployed, miners, fur workers, lumberjacks, teachers, salesmen, athletes, dancers, and artists. They established the first racially integrated military unit in U.S. history and were the first to be led by a black commander. At least 60 percent were members of the Young Communist League or CP. "Wobblies" (members of the Industrial Workers of the World or "IWW"), socialists, and the unaffiliated also joined. The Socialists formed their own [Eugene] Debs Column for Spain, but open recruitment brought on government suppression.
Because the State Department banned all travel to Spain for any potential recruits a lot of volunteers ended up in Britain before taking underground roundabout trails into Spain to join up with the Brigades.
This is a picture of an unidentified Black soldier who the Spanish Authorities were trying to trace prior to a visit by Barack Obama to Spain. "All we know is that he arrived with the Abraham Lincoln Brigade of American volunteers and that he died in the battle at Brunete [in July 1937]," said Sergi Centelles, whose father, Agustí, took the picture.".As far as i know the soldier has not been identified yet, though some authorities have narrowed it down to two possible candidates."The photograph remained hidden for four decades after Agustí Centelles, known as the "Spanish Robert Capa", fled Spain as Franco's forces looked set to win the civil war in 1939."
You can get the full story in this excellent Guardian Article.
And here is a very disturbing tale about the highly disputed accounts of Oliver Law ( pictured at the top of the post) , who became for a short while the only Black Commander of a Company of mixed Black and White US personnel at a time when the Official US Army had segregated units , some of whom were not even recognised or decorated for service in WW2 until the 1990s and in some cases only in the 21st Century.
The brilliant hard hitting in-depth documentary traces the History of the Abraham Lincoln Brigade in its brave fight to aid the democratically elected Spanish Government and against the Mussolini and Hitler supported Franco Military Uprising.(It comes in 12 parts and features the legendary Salaria Kea ).