The eastern half of Poland known as the Kresy, was annexed into the Soviet republics of Ukraine, Belarus, and Lithuania. After Germany terminated the Hitler-Stalin pact and invaded the Soviet Union in June 1941, Poland was completely occupied by German troops.
The Poles formed an underground resistance movement and a government in exile, first in [[Paris]] and later in [[London]], which was recognized by the Western powers. During World War II, 400,000 Poles fought in the [[Polish Home Peoples Army ]] under Soviet command, whereas 200,000 went into combat on Western fronts served in units the [[Polish Home Army]] in underground resistance in Poland, North Africa, Italy, and the Western front and remained loyal to the Free Polish government in exile.
After the German military announced that they had discovered mass graves of murdered Polish army officers at [[Katyn]] in April 1943, the Soviet Union broke relations with the Polish government in exile. The Soviets claimed that the Poles had insulted them by requesting that the [[Red Cross]] investigate these reports. In July 1944, the Soviet Red Army entered Poland and established a communist-controlled "Polish Committee of National Liberation" (PKWN) at Lublin.