From Wikipedia

The Russian German War

 The battles on the "Eastern Front" constituted the largest military confrontation in history. They were characterised by unprecedented ferocity, wholesale destruction, mass deportations, and immense loss of life variously due to combat, starvation, disease, and massacres. The Eastern Front, as the site of nearly all extermination camps, death marches, ghettos, and the majority of pogroms, was central to the Holocaust. Of the estimated 70 million deaths attributed to World War II, over 30 million, many of them civilians, died on the Eastern Front. The Eastern Front was decisive in determining the outcome of World War II, eventually serving as the main reason for Germany's defeat. It resulted in the destruction of the Third Reich, the partition of Germany and the rise of the Soviet Union as a military and industrial superpower.