http://www.spartacus.schoolnet.co.uk/SPguernica.htm
Quoted:
On the outbreak of the Spanish Civil War Guernica had a population of about 7,000 people. On 26th April 1937, Guernica was bombed by the German Condor Legion.
…
General Francisco Franco denied that he had nothing to do with the raid and claimed that the town had been dynamited and then burnt by Anarchist Brigades. After the war a telegram sent from Franco’s headquarters was discovered and revealled that he had asked the German Condor Legion to carry out the attack on Guernica. It is believed that the attack was an attempt to demoralize the Basque people.
End quote