When the Nazis decided to wade into the Spanish Civil War in 1937 in support of their fascist ally Francisco Franco, they did so by dropping bombs indiscriminately on the Basque town of Guernica. No distinction was made by those flying overhead between civilians and militants: many hundreds died, most of them women and children. It was a bitter foretaste of what was to come. In the years which followed, civilian bombing became a hallmark of the changing face of modern warfare, the term blitzkrieg soon entering international parlance. Sotheby’s unveils masterpieces by Monet, Picasso, and Bacon …