Slate has a nice political history of Guernica. (In case you missed it, the UN covered up their copy for Powell’s speech!)
Guernica is no stranger to political dispute. Picasso painted it for the Spanish Pavilion of the 1937 Paris World’s Fair as the fulfillment of a commission that predated the bombing atrocity. After the World’s Fair, Guernica toured European capitals, a rallying-cry-in-paint to the anti-fascist cause. In 1939, the mural and supporting studies arrived in New York for a fund-raising tour in aid of Spanish war relief. It left America for numerous exhibitions during the Cold War years (by which time Picasso had joined the French Communist Party) but during that time the Museum of Modern Art had become its semipermanent home. Meanwhile, the Franco regime, far from viewing the work as an embarrassment, was calling for its “return” to Spain—ignoring the fact that the painting had never actually resided there.