In order to cooperate with the Soviet Union , after Operation Barbarossa an important war ally of the West , Sikorski negotiated in Moscow with Joseph Stalin and they agreed to form a Polish army in the Soviet Union , intended to fight on the Eastern Front alongside the Soviets . The " Anders ' Army " was instead taken to the Middle East and then to Italy . Further efforts to continue the Polish-Soviet cooperation had failed because of disagreements over the borders , the discovery of the Katyn massacre of Polish POWs perpetrated by the Soviets , and the death of General Sikorski . Afterwards , in a process seen by many Poles as a Western betrayal , the Polish Government-in-Exile gradually ceased being a recognized partner in the Allied coalition
Katyn massacre
Katyn massacre
History of Poland (1939–1945)