The Spanish Civil War (1936 -1939) was a clash between the two most dominant political groups in Spain, the Republicans who advocated for a democracy without a monarchy and the Nationalists who encompassed all the right-wing groups such as monarchists, conservatives, etc. The war broke out as the people opposed to the Second Republic, installed in 1931, seemed, in their opinion, to be taking a socialist turn. This division of the Spanish population between those who defended the republic and those who opposed it attracted allies from abroad. The Soviet Union and free thinkers from democratic countries like Britain, France, the U.S. (famous U.S. write Ernest Hemingway participated), etc. joined the side of the Republicans. On the other hand, countries ruled by right-wing dictatorships such as Hitler's Nazi Germany and Mussolini's Fascist Italy aided the Nationalists.
For the Soviets, Germans and Italians, the Spanish Civil War battlefields served as a testing ground for their latest military tactics and designs in tanks, artillery, and especially, aviation. Most of the military equipment tested in Spain would see combat during World War Ii a few years later.
Among the nationalist band, a general would stand out in the eyes of the Nazi Germans: General Francisco Franco. Franco's way of thinking seemed to march Nazi ideology pretty well, so the Germans decided to back him up so that he could become supreme commander of the Nationalist Army.
The fate of the war was decided on behalf of the Nationalists because nearly all the units in the Spanish army held a right wing ideology, and were among the first groups to rebel against the republic. Furthermore, the great support of the Germans in equipment and "advisers" German servicemen whose role was to train Nationalist soldiers, yet they often take direct part in combat) and the lack of help from abroad due to Britain and France's strict neutrality policy would make the Nationalists defeat the Republicans in April 1939 and place Generalissimo Franco as dictator of Spain.