Pitting fascists and communists in a showdown for supremacy, the Spanish Civil War has long been seen as a grim dress rehearsal for World War II. Francisco Franco's Nationalists prevailed with German and Italian military assistance--a clear instance, it seemed, of like-minded regimes joining forces in the fight against global Bolshevism. In Hitler's Shadow Empire Pierpaolo Barbieri revises this standard account of Axis intervention in the Spanish...