On April 26, 1937, the Basque town of Guernica was subjected to a devastating aerial bombardment by the Nazi German Condor Legion and Fascist Italian Aviazione Legionaria, acting in support of Franco's Nationalist forces. The bombing, which lasted for over three hours, destroyed 85 percent of the town's buildings and killed an estimated 150 to 1,654 civilians in one of the first examples of carpet bombing of a civilian population. The attack was intended to break Basque resistance and became a global symbol of the horrors of modern warfare.

The bombing of Guernica inspired some of the most powerful poetry of the Spanish Civil War, including works by Pablo Neruda, W.H. Auden, and many others who denounced the atrocity. The event also inspired Pablo Picasso's monumental painting 'Guernica,' which became the visual emblem of anti-fascist art. The poetry of Guernica emphasized the vulnerability of civilians in modern war and the moral bankruptcy of fascism, themes that would resonate through the poetry of World War II.