Before the German invasion, Ukraine was a constituent republic of the Soviet Union, inhabited by Ukrainians with Russian, Polish, Jewish, Belarusian, German, Romani and Crimean Tatar minorities. It was a key subject of Nazi planning for the post-war expansion of the German state. The Nazi occupation of Ukraine ended the lives of millions of civilians in The Holocaust and other Nazi mass killings: it is estimated 900,000 to 1.6 million Jews and 3 to 4 million non-Jewish Ukrainians were killed during the occupation; other sources estimate that 5.2 million Ukrainian civilians (of all ethnic groups) perished due to crimes against humanity, war-related disease, and famine amounting to more than 12% of Ukraine's population at the time.