Belorussian Offensive Operation (November 1943–February 1944) partition between Berlin and Moscow under terms of the Nazi–Soviet Pact (August 23, 1939), Western Belorussia was annexed to the Soviet Union in September 1939 Its ethnically mixed population was immediately subjected to terrors of the NKVD and, thereafter, to conscription into the Red Army All Belorussia was overrun during the course of BARBAROSSA ( June–December, 1941) It was occupied until July 1944, as part of the Nazi administrative region known as the Reichskommissariat Ostland Belorussia was liberated after heavy and massively destructive fighting, but not until after failure of the Belorussian offensive operation (November 1943–February 1944) The NKVD returned in the wake of the Red Army, bringing renewed misery to a benighted land already denuded of Jews by the Germans and about to see its ethnic Polish population expelled westward by Stalin Belorussian casualties are not precisely known, but probably reached two million out of a prewar population of eight million See also BAGRATION; concentration camps; Holocaust; Katyn massacre; partisans; Red Army BELORUSSIAN OFFENSIVE OPERATION ( JUNE 22–AUGUST 19, 1944) See BAGRATION BELORUSSIAN OFFENSIVE OPERATION (NOVEMBER 1943–FEBRUARY 1944) Several Soviet efforts to retake Belorussia failed in late 1943 and early 1944, despite engaging several large Fronts on the Soviet side Not much is known in general literature beyond the fact that fighting was hard and sustained and that the offensives failed A planned airborne component was canceled due to bad weather, while poor winter conditions also hampered Red Army operations By all accounts, German resistance was fierce, skillful, and successful The Germans defended against a series of linked but poorly implemented attacks by the 1st Baltic, Western, and Belorussian Fronts Operations by Western Front fared especially badly The liberation of Belorussia was thus postponed until July 1944 In the meantime, German killing of Jews and partisans continued behind the lines Soviet killing of accused collaborators and internal purges and deportations of local nationalists resumed wherever the Red Army advanced, until Moscow reclaimed all lands up to the expanded frontier agreed in the Nazi–Soviet Pact of August 23, 1939 BELSEN See Bergen-Belsen BELZEC A concentration camp in Poland sited to take advantage of transportation provided by the Lublin-Lvov railway Opened as a labor camp in 1940, mass killings began in Belzec on March 17, 1942 Redesigned as a full death camp, it remained disguised as a slave labor camp The murderers of Belzec originally used three wooden gas chambers employing a gas produced by petroleum products rather than Zyclon-B The early wooden gas chambers were later replaced by six 152