In 1940, the OUN split into two parts. The older, more moderate members supported Andriy Atanasovych Melnyk and the OUN-M, while the younger and more radical members supported Stepan Bandera's OUN-B. After the start of the Axis invasion of the Soviet Union on 22 June 1941 (Operation Barbarossa), the OUN-B in the person of Yaroslav Stetsko declared an independent Ukrainian state on 30 June 1941 in occupied Lviv, while the region was under the control of Nazi Germany, pledging loyalty to Adolf Hitler. In response, the Nazi authorities suppressed the OUN leadership. In October 1942 the OUN-B established the Ukrainian Insurgent Army (UPA). In 1943–1944, in order to pre-empt Polish efforts at re-establishing Poland's pre-war borders, UPA military units carried out large-scale ethnic cleansing against Polish people. Historians estimate that 100,000 Polish civilians were massacred in Volhynia and Eastern Galicia.