Book excerpt: The role of the great powers in the Spanish Civil War and the war on land that they were able to influence has been much studied. What has not been studied or well understood to a great extent is the role that naval power played and its decisive influence on the war fought on the Iberian Peninsula. To appreciate how the rebels (or Nationalists) were able to overthrow a left of center but very much democratically elected government (the Republicans) it is important to understand the role that sea power played. Spain historically has been very dependent upon imports and diligently maintained sea lines of communication with a relatively strong navy. When the government was not quickly overthrown in a coup, the coup degenerated into a war of attrition. Accordingly, each side quickly became dependent upon the importation of war materials. Should either the Republicans or Nationalists not be able to maintain their sea lines of communication, the war would be lost despite the valiant efforts of the soldiers on land. Fundamentally, the government of Spain, the Republic, lost the Spanish Civil War because they were not able to control the seas and maintain the sea lines of communication.