Avanti in 1921 and had become acquainted with Léon Blum, Marcel Cachin, Romain Rolland and Georges Sorel. During his Parisian exile, Nenni made a decisive contribution to the survival of the Italian Socialist Party, which had moved abroad, and he worked for an alliance between the various anti-fascist parties which had been driven into exile. In 1935, he helped lead the Italian opposition to Mussolini's invasion of Ethiopia. Nenni went on to fight with the International Brigades in the Spanish Civil War. He was the co-founder and the political commissar of the Garibaldi Brigade. After the defeat of the Spanish Republic and the victory of General Francisco Franco he returned to France. In 1943, he was arrested by the Germans in Vichy France and then imprisoned in Italy on the island of Ponza. Nenni's third daughter, Vittoria, was active in the French resistance. She was captured and deported to Auschwitz, where she was murdered on 25 July 1943, aged 28. After being liberated in August 1943, he returned to Rome to lead the Italian Socialist Party, which had been reunified as the Italian Socialist Party of Proletarian Unity. After the surrender of Italy with the Allied armed forces on 8 September 1943, he was one of the political officials of the National Liberation Committee, the underground political entity of Italian Partisans during the German occupation. Postwar politics In 1944, he became the national secretary of the PSI again, favoring close ties between his party and the PCI. After the Liberation, he took up government responsibilities, becoming Deputy Prime Minister and Minister for the Constituent Assembly in the government of Ferruccio Parri and the first government of Alcide De Gasperi. He was Minister for the Constitution, and in October 1946 he became Minister for Foreign Affairs in the second De Gasperi government. The close ties between the PSI and the PCI caused the Giuseppe Saragat-led anti-communist wing of the PSI to leave and form the Italian Socialist Workers' Party in 1947 (later merged into the Italian Democratic Socialist Party, PSDI). During the early stage of the cold war he opposed Italy's entry into NATO fearing that it could drag the country into a war between the two Superpowers and reignite the Italian civil war and instead favoured a policy of Neutrality. In 1951 he was awarded the Stalin peace prize. In 1956, Nenni broke with the PCI after Soviet Union's invasion