When the Germans attacked Poland, Sikorski was still without assignment. With the military defeat of his country and internment of the Polish government in Romania, Sikorski arrived in Paris on 24 September. There he became prime minister and minister for military affairs of the newly formed government-in-exile. As supreme commander of the Polish armed forces, Sikorski reorganized those men who reached France. When France was defeated in June 1940, Sikorski convinced British Prime Minister Winston L. S. Churchill to evacuate the Polish troops and the government-in-exile to Great Britain.
Sikorski pushed for the reestablishment after the war of the Polish state in its pre–September 1939 frontiers, and he outlined plans for a Polish-Czech federation. This position was compromised by the fact that Sikorski represented a defeated country, depending on the goodwill of its western allies. Under these circumstances, Sikorski's attempts to normalize Polish-Soviet relations met with difficulties that were only partly resolved following Germany's invasion of the Soviet Union. Relations between the government-in-exile and Moscow then became impossible with the revelation of the Soviet massacre of Polish army officers in the Katyn Forest.
In the midst of this crisis, Sikorski was killed in a plane crash at Gibraltar on 4 July 1943; he had been returning to Britain from an inspection of Polish troops in the Middle East. He was succeeded in authority by much less able men, but in any case the situation for Poland would have been impossible, given the decision by Britain and the United States to maintain harmonious relations with the Soviet Union. Pascal Trees
Korpalska, Walentyna. Wladyslaw Eugeniusz Sikorski: Biografia polityczna. Wroclaw: Ossolineum, 1981.; Sword, Keith, ed. Sikorski: Soldier and Statesman: A Collection of Essays. London: Orbis Books, 1990.; Waszak, Leon. Agreement in Principle: The Wartime Partnership of General Wladyslaw Sikorski and Winston Churchill. New York: Peter Lang, 1996.