Spanish Civil War
The failed 1936 coup that became a three-year war, a testing ground for German and Italian weapons, and proof that Britain and France would not fight.
On 17 and 18 July 1936 a group of Spanish generals tried to overthrow the elected government. The coup worked in about half the country and failed in the other half, and that failure turned it into a three-year war that killed roughly half a million people. By April 1939 Francisco Franco ruled Spain, and he ruled it until he died in 1975.
Spain in the 1930s was arguing about everything at once: who owned the land in a countryside full of landless laborers, how much power the Church should have, whether Catalonia and the Basque provinces could govern themselves, and whether the army answered to civilians. The Republic, proclaimed in 1931, swung left, then right, then left again when the Popular Front won narrowly in February 1936. By then both sides had decided the other could not be allowed to govern at all.
A Spanish war fought with foreign weapons
The first decisive moment was a logistics problem. Franco's Army of Africa, the best troops in Spain, was stuck in Morocco because the navy had stayed loyal to the government. Hitler and Mussolini sent the transport aircraft that flew them across the strait, one of the first military airlifts in history.
After that, foreign powers ran much of the war. Germany sent the Condor Legion and used Spain to test dive bombers, radios, and the bombing of towns. Its destruction of Guernica on 26 April 1937 gave Picasso his subject and gave Europe a preview of what was coming. Italy sent about 75,000 ground troops. The Soviet Union sent aircraft, tanks, and advisers, and charged for them out of the Spanish gold reserve, most of which was shipped to Moscow and never came back. The Comintern recruited the International Brigades, roughly 35,000 foreign volunteers.
Britain and France set up a Non-Intervention Committee, which Germany, Italy, and the Soviet Union all joined and ignored. In practice non-intervention meant the legal government could not buy weapons while its enemies were resupplied continuously.
The war inside the Republic
The Republican side also fought itself. Communists, armed by Moscow and determined to run a conventional war, moved against the anarchists and the anti-Stalinist party POUM. Street fighting in Barcelona in May 1937 ended with POUM banned and its leader Andres Nin murdered. George Orwell fought in that militia, was nearly arrested in the purge, and wrote Homage to Catalonia about it. What he saw there produced Animal Farm and 1984.
Franco moved slowly and never had that problem. He unified his side by force, took ground, and eliminated opposition as he went. After the Republic's last offensive on the Ebro failed in late 1938, Barcelona fell in January 1939 and Madrid in March.
Afterwards
The killing did not stop with the fighting. Tens of thousands were executed or died in prison in the years after 1939, and hundreds of thousands fled into exile. Spain stayed formally neutral in the Second World War while sending volunteers to fight for Germany in Russia.
Most observers drew military lessons from Spain and got them wrong, deciding that bombers would flatten cities and that tanks worked best spread among the infantry. The Germans, who had been there, concluded the opposite about tanks. The lesson that actually mattered was political, and Hitler read it correctly: when force was used openly in 1936, Britain and France chose not to respond.