The War in the North was the campaign of the Spanish Civil War in which the Nationalist forces defeated and occupied the parts of northern Spain that had remained loyal to the Republican government. The campaign included several separate battles. The Biscay Campaign resulted in the loss of the part of the Basque Country still held by the Republic and Bilbao, the greatest Spanish industrial centre. That part of the campaign saw the Bombing of Guernica and Durango. The Battle of Santander caused the loss of the province of Santander in Cantabrian Castile for the Republic. The Battle of El Mazuco led to the capture of the Republican-controlled part of Asturias and the fall of Gijón, the Republic's last northern stronghold, to the Nationalists. The campaign ended on October 21, 1937 with a decisive and total Nationalist victory. Background On the Nationalist takeover of Navarre in July 1936, General Mola had announced a war of extermination and no mercy to any dissent. Harsh repression started to be implemented against those blacklisted, who were Navarrese individuals and their families, and by late August, the Requeté, a Carlist militia, from Navarre advanced towards Irun with a mission to cut off Gipuzkoa's Republican forces from the French border. After the fall of Irun and then of San Sebastián, on September 23, 1936, the Nationalists, led by Francisco Franco, pushed their way through Gipuzkoa and cut off the Republican-controlled areas in northern Spain from the border with France. That area had been already isolated from the rest of Spain by Nationalist control at the beginning of the war. The area was very attractive to the Nationalists because of the industrial production of Biscay and the mineral resources of Asturias. The conquest and the control of the area would be profitable because of its valuable resources and would also expel Republican forces and concentrate large numbers of Nationalist troops to force a two-front war. Franco realised that Madrid, the capital, was not going to be conquered quickly but that Basque resources of iron, coal, steel and chemicals were a tempting target. The northern Republicans were also politically divided and weakened by struggles between Basque nationalists and leftists. Furthermore, its major supplies came by sea. Franco ordered his commanders on the Madrid front to go on the defensive and to send all available resources to the north. Republican forces attempted to establish a front at Buruntza.