Seventy-five years ago, the Spanish town of Guernica was bombed into rubble. The brutal act propelled one of the world’s greatest artists into a three-week painting frenzy. Pablo Picasso’s “Guernica” starkly depicts the horrors of war, etched into the faces of the people and the animals on the 20-by-30-foot canvas. It would not prove to be the worst attack during the Spanish Civil War, but it became the most famous, through the power of art. The impact of the thousands of bombs dropped on Guernica, of the aircraft machine guns strafing civilians trying to flee the inferno, is still felt to this day—by the elderly survivors, who will eagerly share their vivid memories, as well as by Guernica’s youth, who are struggling to forge a future for their town out of its painful history.

The German Luftwaffe’s Condor Legion did the bombing at the request of Gen. Francisco Franco, who led a military rebellion against Spain’s democratically elected government. Franco enlisted the help of Adolf Hitler and Benito Mussolini, who were eager to practice modern techniques of warfare on the defenseless citizens of Spain. The bombing of Guernica was the first complete destruction by aerial bombardment of a civilian city in European history. While homes and shops were destroyed, several arms-manufacturing facilities, along with a key bridge and the rail line, were left intact.

Spry and alert at 89, Luis Iriondo Aurtenetxea sat down with me in the offices of Gernika Gogoratuz, which means “Remembering Gernika” in the Basque language. Basque is an ancient language and is ...