May 11, 1937, Saturday, a gigantic demonstration in Paris of more than one million persons repudiated the barbarian I bombard air committed by the German aviation on Guernica, the oldest town of the Basques and the center of its cultural tradition. Picasso did not respond to the demonstration. It remained in its study where painted, caught a small notebook of blue leaves and gave the first step in the gestation of the Guernica. .
Four months before Max Aub, Jose Gaos and other intellectual Spaniards had asked to Picasso that to contribute with a mural one al Spanish building of the Universal Exposition that would be inaugurated in Paris the month of June. Spain was in war since six months ago and the exposition was an exceptional occasion to defend the ideals of the Republic and to denounce the violence that sufrí the Spanish town. .
The to read of the bombardment and the destruction of Guernica, provided to Picasso the necessary spirit to start. From May to October Picasso carried out approximately sixty sketchs or studies. One of the scenes that more drew went that of the mother that cries for its dead son. .
Friday 28 of May Max Aub writes Luis Araquistain: "This tomorrow I arrived at an agreement with Picasso. I have been able to convince him, and of this luck, I have extended it a check by value of 150,000 Frank French, by the ones that the corresponding receipt has signed me. Although this sum has more well a symbolic character, given the value inapreciable of the cloth in question, represents, nevertheless, practically an acquisition of the same one on the part of the Republic. I reckon that this formula was the most convenient one to claim the right of property of the cited picture." .
July 12, seven weeks after inaugurated the exposition, the mural one was installed in the main patio of the Spanish building, and set against him, another with the face of Federico Garcia Lorca, poet and Spanish playwright executed in 1936.