World War Two was the deadliest conflict in human history with approximately 60 million deaths even according to lower estimates. As this graph makes clear, the USSR was particularly affected by the war. It suffered badly both in military confrontation and killings of civilians, including 1 million victims of the Holocaust.
The figures for civilian casualties do not include deaths from war-related famine and associated illnesses which killed huge numbers in India, China, Greece, Germany, the USSR, the Philippines and the French and Dutch Pacific Colonies. These graphs also exclude many countries which were colonies during the war.