What country had the largest number of casualties in World War 2?

The Soviet Union suffered the largest number of casualties in World War II, with estimates ranging from 20 million to over 27 million people, including both military personnel and civilians. The immense loss was due to various factors, including brutal combat on the Eastern Front, widespread atrocities, and the impact of the Nazi invasion. This staggering toll significantly shaped the post-war landscape and the Soviet Union's role in global politics.