Combining military, political, cultural, social, and oral history, Sebastian Balfour narrates for the first time the development of a brutalized, interventionist army that played a crucial role in the victory of the Francoists in the Spanish Civil War. Spain's new colonial venture in Morocco in the early twentieth-century turned into a bloody war against the tribes resisting the Spanish invasion of their lands. After suffering a succession of heavy military disasters against some of the most accomplished guerrillas in the world, the Spanish army turned to chemical warfare and dropped massive quantities of mustard gas on civilians.

Sebastian Balfour exposes this previously closely guarded secret using evidence from Spanish military archives and from survivors in Morocco. He also narrates the daily life of soldiers in the war as well as the self-images and tensions among the colonial officers. After looking at the motives that drove Moroccans to resist or cooperate with Spain, the author describes the contradictory pictures among Spaniards of Moroccan collaborators and foes. Finally, he examines the Spanish colonial army's response to the Second Republic of 1931-1936 and its brutal march through Spain in the Civil War.