Estimates for the total casualties of the war vary, because many deaths went unrecorded. Most suggest that some 75 million people died in the war, including about 20 million military personnel and 40 million civilians. Many of the civilians died because of deliberate genocide, massacre, mass-bombing, disease and starvation. The Soviet Union lost around 27 million people during the war, including 8.7 million military and 19 million civilian deaths. The largest portion of military dead were 5.7 million ethnic Russians, followed by 1.3 million ethnic Ukrainians. A quarter of the people in the Soviet Union were wounded or killed. Germany sustained 5.3 million military losses, mostly on the Eastern Front and during the final battles in Germany.
Of the total deaths in World War II, approximately 85 percent—mostly Soviet and Chinese—were on the Allied side and 15 percent on the Axis side. Many of these deaths were caused by war crimes committed by German and Japanese forces in occupied territories. An estimated 11 to 17 million civilians died as a direct or indirect result of Nazi ideological policies, including the systematic genocide of around 6 million Jews during the holocaust, along with a further 5 to 6 million ethnic Poles and other Slavs (including Ukrainians and Belarusians, Roma, homosexuals, and other ethnic and minority groups. Hundreds of thousands (varying estimates) of ethnic Serbs, along with gypsies and Jews, were murdered by the Axis-aligned Croatian Ustase in Yugoslavia, with retribution-related killings just after the war ended.
Chinese civilians being buried alive by soldiers of the Imperial Japanese Army, during the Nanking Massacre, December 1937
The best-known Japanese atrocity was the Nanking Massacre, in which several hundred thousand Chinese civilians were raped and murdered. Between 3 million to more than 10 million civilians, mostly Chinese (estimated at 7.5 million), were killed by the Japanese occupation forces. Mitsuyoshi Himeta reported 2.7 million casualties occurred during the Sankö Sakusen. General Yasugi Okamura implemented the policy in Heipei and Shantung. Okamura was convicted for war crimes in July 1948 by the Nanjing War Crimes Tribunal but was immediately protected by the personal order of Nationalist leader Chiang Kai-shek. He returned to Japan in 1949 and died on 02-09-1966, age 82 in Tokyo..
Axis forces employed biological weapons and chemical weapons. The Imperial Japanese Army used a variety of such weapons during their invasion and occupation of China and in early conflicts against the Soviets. Both the Germans and Japanese tested such weapons against civilians and, sometimes on prisoners of war. Distressing that Japan was put across one’s knees by two atomic bombs and 240.000 prospectless civilian death.
The Soviet Union was responsible for the Katyn massacre of 22.000 Polish officers, and the imprisonment or execution of thousands of political prisoners by the NKVD, in the Baltic states, and eastern Poland annexed by the Red Army.
The mass-bombing of civilian areas, notably the cities of Warsaw , Rotterdam, and London; including the aerial targeting of hospitals and fleeing refugees by the German Luftwaffe, along with the bombing of Tokyo, and German cities of Dresden, Hamburg, and Cologne, by the Western Allies may be considered as war crimes. The latter resulted in the destruction of more than 160 cities and the deaths of more than 600.000 German civilians. However, no positive or specific customary international law with respect to aerial warfare existed before or during World War II.