Interwar Europe was not an interlude of complete peace between the two World Wars. Most importantly, the Spanish Civil War broke out in 1936, three years before Germany invaded Poland. That war saw the Nationalists under Francisco Franco defeat the Republicans, who lacked a single leader. Critical to the Nationalist victory was German support which began on July 26th, 1936, when Adolf Hitler decided to intervene.
Early German intervention in the Spanish Civil War took the form of transporting Nationalist troops from Spanish holdings in Africa to mainland Spain. The soldiers from the Army of Africa were vital to Franco’s war effort during the first year of the war, and allowed the Nationalists to consolidate their hold over Northern and Western Spain. By October, however, the focus had shifted towards providing direct air support for the Nationalists. The Germans also shipped weapons and supplies to Spain. A major reason for German support was that the Soviets were providing arms and air support to the Republicans. The Republicans were not a unified front, and as the war dragged on the Communist factions gained ever more influence, partly due to Soviet efforts. German air volunteer forces were consolidated into the Condor Legion, which became vital to Franco’s war effort. Fascist Italy also sent volunteers, and unlike Germany it sent significant ground combat units. These units generally performed poorly, however, against Republicans armed with Soviet tanks which outmatched lighter Italian models. The Germans gained valuable air warfare experience, and used the Spanish Civil War as an opportunity to test the effectiveness of strategic bombing on cities, most notably during the bombing of Guernica. While at its height the Condor Legion made up more than a fifth of the total Nationalist air forces, the training and advice provided by German officers may have been more important than the air operations themselves. The untrained Nationalist militias and inexperienced officers were turned into a semi-effective fighting force in large part thanks to German military attaches. Regardless, German volunteers provided vital intelligence and training which facilitated several successful offensives that secured a Nationalist victory. The Civil War ended in April of 1939, and by May the volunteers had returned to Germany.
The German intervention in the Spanish Civil War most likely was decisive to the outcome. Without German transports, the Nationalists never would have survived the initial months of the conflict. Further, German training and air support was critical to the offensives on Madrid, Barcelona, and the Basque country that concluded the war in the Nationalists’s favor. The future of Spain was thus determined in large part by a few thousand German volunteers and a few hundred planes.