The Spanish Civil War was a major conflict in Spain that started after an attempted coup d'état committed by parts of the army against the government of the Second Spanish Republic. The Civil War devastated Spain from July 17, 1936 to April 1, 1939, ending with the victory of the rebels and the founding of a dictatorship led by the Nationalist General Francisco Franco.
The participation of the Soviet Union, Germany and Italy in providing arms and personnel made the Spanish Civil War a proxy war between two sides that would later clash during World War II.
The Spanish Civil War that had begun in July 1936 was still being waged with ferocious intensity two years later when a general Europeanwar broke out over the Sudetenland crisis. As a result of the new great war, Britain and France opened up the supply lines to the Spanish Republicans, and the armies facing José Sanjuro's men began receiving better weapons.
This timeline already diverged from ours in 1936, with Sanjurjo surviving the accident where he was killed in OTL and leading the Nationalist forces, rather than Franco. However, the book makes clear that until September 1938 this made little difference to the conduct of the war, and that Sanjurjo made much the same political and military decisions which Franco would have made. Specifically, both the Nationalist offensive reaching the sea in April and the Republican counter-offensive across the Ebro in July are seen as having taken place in virtually the same way as in OTL, despite the difference in the Nationalist supreme command.
The conduct of Sanjurjo clearly diverges from Franco's only later on, in early 1939, when Sanjurjo embarks on the conquest of Gibraltar and thus makes Britain into Nationalist Spain's staunch foe. In OTL, Franco avoided any step against Gibralter even when repeatedly urged to it by Germany, kept Nationalist Spain neutral in the larger war and retained his open channels to the British – which ensured his survival in the post-war world.