Complex sentence: Between 1941 and 1944, the German invasion of the Soviet Union caused its defacto dissolution, however with the retreat of the Germans in 1944-1945, Soviet hegemony was re-established.
Split into simpler sentences: Between 1941 and 1944, the German invasion of the Soviet Union caused its defacto dissolution. However, with the retreat of the Germans in 1944-1945, Soviet hegemony was re-established.