______The 1936 election of the leftist "Popular Front" in Spain led to a civil war between the right-wing Nationalists and the left-wing Republicans. During the war the Nationalists would get help from the fascist regimes of Italy and Germany. The Republicans got help from the USSR and from the Communist International.
______European and American leftists who volunteered to fight for Republican Spain were organized into the International Brigades by the Comintern, which for the sake of command-and-control were further broken down into battalions of volunteers who spoke the same language or had the same national background. The Brigades followed the Soviet "mixed-brigade" model that incorporated infantry battalions with supporting artillery batteries and specialized companies. Communists, socialists and liberals from Germany, France, Belgium, Poland, Hungary, Yugoslavia, Italy, Czechoslovakia, Bulgaria, Britain and the United States all made their way to Spain "to fight fascism" under the symbol of the three-pointed red star.
______The strange thing was, the International Brigades were organized along the same lines as the Red Army, right down to having commissars, or political officers, assigned to each commander to ensure that any decision made was not just tactically correct but politically correct as well. American soldiers in the Abraham Lincoln and Washington Battalions addressed each other as "comrade." Early on, Spain's new People's Republic Army was showing the influence of its Soviet advisors.
______The International Brigades became the shock troops of the Republicans. Although by the end of the war the ranks of most of their battalions were heavily augmented with Spanish volunteers, the Brigades fought well at Brunete, Jarama, Teruel, Aragon and on the Ebro. This despite the occasional purge to "liquidate" a Trotskyite or two.
______Nevertheless, the Republicans decided to disband the International Brigades and send the volunteers home in September 1938. It was hoped that that the plight of Spain fighting alone against Fascism would arouse the League of Nations to action and make the Nationalists get rid of their German and Italian "volunteers." It didn't work; relying on action by the League was pretty much the same as waiting for the UN to take action. By March 1939 the war was over.
______Both sides learned lessons: the Germans learned the right ones and the Russians learned the wrong ones. Thanks to their experiences in Spain the Germans were able to perfect the Blitzkrieg doctrine that they would use to overrun most of Europe. The Russians would learn that you could keep the system of political indoctrination and purges in place, even while fighting a war!