Excerpts from Books and Wikipedia
"The bombing of Guernica served no strategic purpose in the Spanish Civil War. Franco's real aim was to destroy Basque nationalism… General Franco denied the attack; then he blamed the Basque themselves. But four foreign journalists were in the region, and the truth was soon out. World opinion was shocked. Certainly Picasso was horrified: his gory masterpiece was completed two months later." [1001 Days]