Fascism was on the rise in the 1930s; a second world war seemed the inevitable culmination of tense divisions within Europe between opposing Fascist and anti-Fascist camps. In this atmosphere of political strife, Picasso began to look for ways to imbue the heretofore private symbols in his art with new, public meanings, to look for a way in which his work could contribute to the cause of the Left. On July 14, 1936, Picasso contributed to festivities organized by Popular Front (a coalition of Socialists and Communists) in celebration of the anniversary of the French Revolution; an enlarged version of an earlier painting on the theme of the Minotaur was used as the curtain for Romain Rolland's play Le 14 juillet. In this context, Picasso's work took on a political significance, and this significance energized his work.

The Spanish Civil War broke out just a few days later, on July 18, 1936. The Republican government appointed Picasso director of the Prado museum; Picasso etched a sort of Cubist comic strip called "The Dream and Lie of Franco," portraying the General as a revolting little gnome, and wrote an accompanying poem to be sold for the benefit of the Spanish Republic.

In 1937, the Spanish Republican government asked Picasso to paint a mural for the Spanish pavilion at the Universal Exposition that year in Paris. Inspiration came in April, in the form of the horrific aerial bombing by the Fascists of the town of Guernica. The monumental canvas that resulted– depicting a massacre of the innocents in the black-and-white tones of newspapers and newsreels, and filled with historical and political allusions and expressive force–became an icon and the last real history painting.

Meanwhile, in sunnier America, the Museum of Modern Art in New York (MOMA) was preparing a giant show called Picasso: Forty Years of his Art. Founded in 1929 and supported by the Rockefellers, MOMA played a crucial role in the acceptance of avant-garde art by a wide section of the public. The museum's 1939 acquisition of Picasso's "Les Demoiselles d'Avignon" marked the decisive success of modernism in the marketplace of popular taste; this painting had seemed so cataclysmically radical when it was first painted that it remained in Picasso's studio for years, facing the wall, before being shown at all. Now it was something that the American public could applaud. Public taste had changed drastically over the last few decades. Picasso himself, as the number-one beneficiary of this change in public taste, became very wealthy and acquired the aura of a movie star. He was instantly recognizable (and still is, as evidenced by the use of his image today to market Apple computers–"Think different"). Photographs of him taken by his friend Brassaï in Paris were published in Life magazine in 1939.

Picasso's international reputation probably helped him when Paris was invaded by the Germans in 1940. Although under surveillance, he was allowed to continue with his work. His painting reflected the grim reality of the Occupation; the subject matter of "Aubade," for instance, is a serenade in a harem, but this subject, which he had treated before in a register of joyful sensuality, stands in this work in sharp contrast to its dark treatment. The colors are dull, the shapes angular, the mood claustrophobic.

Picasso tried writing again–this time, a play, called Desire Caught by the Tail, about the grimness of Occupation. When it was given a private reading in 1944, participants included Albert Camus, Simone de Beauvoir, Jean- Paul Sartre, and Dora Maar. While maintaining his affair with Maar, he met a young painter and committed Communist named Françoise Gilot; the two began living together in 1946 and had two children, Claude and Paloma. Picasso's most active period of political involvement coincided with his relationship with Françoise. Soon after the end of the Occupation in 1944, Picasso announced that he had joined the French Communist Party. In the following years, he would paint posters and a portrait of Stalin at the party's request; he accepted the Lenin Peace Prize in 1950. Picasso continued as a party member–though a less active one–even after Gilot, ambitious and sick of life in her famous companion's shadow, left for Paris with the children in 1953.