26 April 1937, a Monday, market day. German and Italian planes bomb Guernica, a Basque town with no garrison worth the name, in waves through the late afternoon. The centre burns. Within weeks Picasso is painting it in black, white and grey, the colours of a newspaper photograph.
Why then
Spain has been at war with itself since July 1936, when army officers, Franco soon at their head, rose against the elected Republic. Hitler and Mussolini send the Nationalists aircraft and troops; Stalin sends the Republic weapons and advisers; volunteers arrive from fifty countries. Franco's northern offensive needs the Basques broken.
What they wanted
Franco is after victory and a warning. The German Condor Legion is testing its bombers and tactics on a live town. The Basques are defending their autonomy and their homes. International volunteers believe history has a right side. Ideology does not stop a bomber.
What changed
The town becomes the century's picture of bombing civilians. Franco wins in 1939, after a war that kills around half a million people, and rules until 1975. Within three years the same air force is over Warsaw and Rotterdam.
Still argued
Franco's side claimed the retreating Basques burned their own town. The German role is now beyond doubt; the death toll is not, with estimates from about 150 to more than 1,600.