prior to the start of world war two, germany and italy practiced many of their modern aerial bombing tactics against the civilian spanish population during their civil war (at the request of fascist spanish side).
one of these bombings was carried out in the spanish town of guernica. the famous painting above is meant to invoke the horrors and intensity of that event.
legend tells of a german officer who pointed to a picture of the guernica painting and asked picasso himself, "Did you do this?"
No. You did.