After the Polish government-in-exile organized the "Anders Army" in 1941 in the Soviet Union in the aftermath of the Operation Barbarossa and evacuated it to the West, Polish communists sought to create a new army, under communist control, out of the many ethnic Poles that remained in the Soviet Union. These were primarily citizens of the prewar Second Polish Republic that had been deported and often imprisoned by the Soviets following the Soviet annexation of Poland's eastern territories, as per the Molotov-Ribbentrop Pact. The Soviet Union created the Union of Polish Patriots (ZPP) in 1943, a communist Polish organization intended to represent the interest of Poles on Soviet soil and organize this new army. The relocated Poles, along with numbers of Byelorussians, Ukrainians, and Polish Jews, were organized into a division, the nucleus of a force known as the Polish People's Army ("Ludowe Wojsko Polskie", LWP) but colloquially known as the "Berling Army" after its first commander, Zygmunt Berling. The division made its combat debut in October 1943 at the Battle of Lenino. Afterwards, it was rapidly expanded into the 1st Polish Corps, which in turn grew by 1944 into the 1st Polish Army. In 1945, 2nd Polish Army was added to the LWP. By the end of the war, the LWP numbered about 200,000 front-line soldiers. The Polish communist guerilla force, the Armia Ludowa, was integrated with the Polish People's Army in January 1944.