In terms of total numbers, the Soviet Union bore an incredible brunt of casualties during WWII. An estimated 16,825,000 people died in the war, over 15% of its population.
Officially, roughly 8.6 million Soviet soldiers died in the course of the war, including millions of POWs.
An estimated 40,000,000 to 50,000,000 people died during World War II. Among the Allied powers, the U.S.S.R. suffered the greatest total number of dead: perhaps 18,000,000.
Hiroshima lost more than 60,000 of its 90,000 buildings, all destroyed or severely damaged by one bomb. In comparison, Nagasaki – though blasted by a bigger bomb on 9 August 1945 (21,000 tonnes of TNT to Hiroshima's 15,000) – lost 19,400 of its 52,000 buildings.
Only 14 countries remained officially neutral throughout the entire war. They included Sweden, Switzerland, Spain, Portugal, Ireland, Turkey, Yemen, Saudi Arabia and Afghanistan as well as the microstates of Andorra, Monaco, Liechtenstein, San Marino and Vatican City.
The Soviet Union suffered the highest number of fatalities of any single nation, with estimates mostly falling between 22 and 27 million deaths. China then suffered the second greatest, at around 20 million, although these figures are less certain and often overlap with the Chinese Civil War.
The Soviet Union lost around 27 million people during the war, including 8.7 million military and 19 million civilians. This represents the most military deaths of any nation by a large margin. Germany sustained 5.3 million military losses, mostly on the Eastern Front and during the final battles in Germany.
World War II losses of the Soviet Union from all related causes were about 27,000,000 both civilian and military, although exact figures are disputed. A figure of 20 million was considered official during the Soviet era.
Although the United States played the dominant role, all three major Allied countries were necessary to victory in Europe. The most important contribution made by Britain was to survive Hitler's onslaught in 1940. Had the British failed to hold off the Nazis, the Second World War would have taken a far different turn.
Russians also point to the fact that Soviet forces killed more German soldiers than their Western counterparts, accounting for 76 percent of Germany's military dead.
By far the most costly war in terms of human life was World War II (1939–45), in which the total number of fatalities, including battle deaths and civilians of all countries, is estimated to have been 56.4 million, assuming 26.6 million Soviet fatalities and 7.8 million Chinese civilians were killed.
*Worldwide casualty estimates vary widely in several sources. The number of civilian deaths in China alone might well be more than 50,000,000.
Among the Axis powers, there were about 4,200,000 German deaths and about 1,972,000 Japanese deaths.
Over the course of the war, 880,000 British forces died, 6% of the adult male population and 12.5% of those serving.
The Operation Meetinghouse firebombing of Tokyo on the night of 9 March 1945 was the single deadliest air raid of World War II, greater than Dresden, Hamburg, Hiroshima, or Nagasaki as single events.
China After World War II
That count includes hundreds of thousands of deaths due to drowning, disease and starvation after the Chinese nationalist army breached massive holes in dikes holding back the Yellow River to stymie the Japanese advance in 1938.
Varying estimates suggest that Russia may have suffered the highest number of military and total fatalities in the First World War.
Battle of Antietam breaks out
Beginning early on the morning of September 17, 1862, Confederate and Union troops in the Civil War clash near Maryland's Antietam Creek in the bloodiest single day in American military history.
But both Hitler and Stalin were outdone by Mao Zedong. From 1958 to 1962, his Great Leap Forward policy led to the deaths of up to 45 million people—easily making it the biggest episode of mass murder ever recorded.
David Hacker conducted further investigations and claimed that the number was closer to 750,000 (and possibly as high as 850,000).
China had been at war with Japan since 1937 and continued the fight until the Japanese surrender in 1945. The United States advised and supported China's ground war, while basing only a few of its own units in China for operations against Japanese forces in the region and Japan itself.
Japan formally surrendered on 2 September 1945. China was recognized as one of the Big Four Allies during the war, regained all territories lost to Japan and became one of the five permanent members of the United Nations Security Council.
Over 87,000 Indian troops, and 3 million civilians died in World War II. Field Marshal Sir Claude Auchinleck, former Commander-in-Chief, India, stated that Britain "couldn't have come through both wars [World War I and II] if they hadn't had the Indian Army."
World War II (1938-1945) – With a death toll between 40 and 85 million, the Second World War was the deadliest and worst war in history. Experts estimate with such a high death toll, about three percent of the world's population in 1940 died.
The longest war in history is believed to be the Reconquista (Spanish for Reconquest), with a duration of 781 years.