Guernica by Pablo Picasso (Credit: Museo Nacional Centro de Arte Reina Sofía) Opening during the Spanish Civil War, the 1937 Paris Exhibition allowed artists to speak out against brutality. Fiona Macdonald looks at a moment when paintings became propaganda. On 26 April 1937, Nazi German and Italian bombers attacked the Basque city of Guernica. Over the course of three hours, they destroyed three-q