コンドル軍団
The Condor Legion persuaded Franco to send troops to go north and to be led by General Emilio Mola. On 31 March 1937, Mola attacked the province of Biscay, which included the bombing of Durango by the Condor Legion. Republicans put up a tough fight against the German troops but eventually were forced back. Many refugees fled to Guernica for safety, about a thousand people turned to Guernica. On 25 April, Mola sent a warning to Franco saying that he was planning a heavy strike against Guernica.