Guernica
was Basque town full of refugees, bombed by Nazis.  Few buildings left standing, 250 dead – one of the first instances of terror bombing, directed at civilians.

Reporting was severely restricted, and it was denied that foreign planes had been used (as Germany had supposedly been neutral).  But the report by George Steer fed outrage internationally.  Picasso refused to let his painting come back to Spain until again a republic (now in Museo Raina Sofia, Madrid).