Casualties and war crimes
Estimates for the total number of casualties in 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.[315][316][317] Many of the civilians died because of deliberate genocide, massacres, mass-bombings, disease, and starvation.
The Soviet Union lost around 27 million people during the war,[318] 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.[319] A quarter of the people in the Soviet Union were wounded or killed.[320] Germany sustained 5.3 million military losses, mostly on the Eastern Front and during the final battles in Germany.[321]
Of the total number of deaths in World War II, approximately 85 percent—mostly Soviet and Chinese—were on the Allied side and 15 percent were 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[322] to 17 million[323] civilians died either as a direct or as an 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)[324]—Roma, homosexuals, and other ethnic and minority groups.[323] Hundreds of thousands (varying estimates) of ethnic Serbs, along with gypsies and Jews, were murdered by the Axis-aligned Croatian Ustaše in Yugoslavia,[325] and retribution-related killings were committed just after the war ended.
In Asia and the Pacific, between 3 million and more than 10 million civilians, mostly Chinese (estimated at 7.5 million[326]), were killed by the Japanese occupation forces.[327] The best-known Japanese atrocity was the Nanking Massacre, in which fifty to three hundred thousand Chinese civilians were raped and murdered.[328] Mitsuyoshi Himeta reported that 2.7 million casualties occurred during the Sankō Sakusen. General Yasuji Okamura implemented the policy in Heipei and Shantung.[329]
Axis forces employed biological and chemical weapons. The Imperial Japanese Army used a variety of such weapons during its invasion and occupation of China (see Unit 731)[330][331] and in early conflicts against the Soviets.[332] Both the Germans and Japanese tested such weapons against civilians[333] and, sometimes on prisoners of war.[334]
The Soviet Union was responsible for the Katyn massacre of 22,000 Polish officers,[335] and the imprisonment or execution of thousands of political prisoners by the NKVD,[336] 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[337] 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 death of more than 600,000 German civilians.[338] However, no positive or specific customary international humanitarian law with respect to aerial warfare existed before or during World War II.[339]
Concentration camps, slave labour, and genocide
The German government led by Adolf Hitler and the Nazi Party was responsible for the Holocaust, the killing of approximately 6 million Jews, as well as 2.7 million ethnic Poles,[340] and 4 million others who were deemed "unworthy of life" (including the disabled and mentally ill, Soviet prisoners of war, homosexuals, Freemasons, Jehovahs Witnesses, and Romani) as part of a programme of deliberate extermination. About 12 million, most of whom were Eastern Europeans, were employed in the German war economy as forced labourers.[341]
In addition to Nazi concentration camps, the Soviet gulags (labour camps) led to the death of citizens of occupied countries such as Poland, Lithuania, Latvia, and Estonia, as well as German prisoners of war (POWs) and even Soviet citizens who had been or were thought to be supporters of the Nazis.[342] Sixty percent of Soviet POWs of the Germans died during the war.[343] Richard Overy gives the number of 5.7 million Soviet POWs. Of those, 57 percent died or were killed, a total of 3.6 million.[344] Soviet ex-POWs and repatriated civilians were treated with great suspicion as potential Nazi collaborators, and some of them were sent to the Gulag upon being checked by the NKVD.[345]
Japanese prisoner-of-war camps, many of which were used as labour camps, also had high death rates. The International Military Tribunal for the Far East found the death rate of Western prisoners was 27.1 percent (for American POWs, 37 percent),[346] seven times that of POWs under the Germans and Italians.[347] While 37,583 prisoners from the UK, 28,500 from the Netherlands, and 14,473 from the United States were released after the surrender of Japan, the number of Chinese released was only 56.[348]
According to historian Zhifen Ju, at least five million Chinese civilians from northern China and Manchukuo were enslaved between 1935 and 1941 by the East Asia Development Board, or Kōain, for work in mines and war industries. After 1942, the number reached 10 million.[349] The US Library of Congress estimates that in Java, between 4 and 10 million romusha (Japanese: "manual laborers"), were forced to work by the Japanese military. About 270,000 of these Javanese labourers were sent to other Japanese-held areas in South East Asia, and only 52,000 were repatriated to Java.[350]
On 19 February 1942, Roosevelt signed Executive Order 9066, interning about 100,000 Japanese living on the West Coast. Canada had a similar program.[351][352] In addition, 14,000 German and Italian citizens who had been assessed as being security risks were also interned.[353]
In accordance with the Allied agreement made at the Yalta Conference millions of POWs and civilians were used as forced labour by the Soviet Union.[354] In Hungarys case, Hungarians were forced to work for the Soviet Union until 1955.[355]
Occupation
In Europe, occupation came under two forms. In Western, Northern and Central Europe (France, Norway, Denmark, the Low Countries, and the annexed portions of Czechoslovakia) Germany established economic policies through which it collected roughly 69.5 billion reichmarks (27.8 billion US Dollars) by the end of the war, this figure does not include the sizeable plunder of industrial products, military equipment, raw materials and other goods.[356] Thus, the income from occupied nations was over 40 percent of the income Germany collected from taxation, a figure which increased to nearly 40 percent of total German income as the war went on.[357]
In the East, the much hoped for bounties of Lebensraum were never attained as fluctuating front-lines and Soviet scorched earth policies denied resources to the German invaders.[358] Unlike in the West, the Nazi racial policy encouraged excessive brutality against what it considered to be the "inferior people" of Slavic descent; most German advances were thus followed by mass executions.[359] Although resistance groups formed in most occupied territories, they did not significantly hamper German operations in either the East[360] or the West[361] until late 1943.
In Asia, Japan termed nations under its occupation as being part of the Greater East Asia Co-Prosperity Sphere, essentially a Japanese hegemony which it claimed was for purposes of liberating colonised peoples.[362] Although Japanese forces were originally welcomed as liberators from European domination in some territories, their excessive brutality turned local public opinion against them within weeks.[363] During Japans initial conquest it captured 4,000,000 barrels (640,000 m3) of oil (~5.5×105 tonnes) left behind by retreating Allied forces, and by 1943 was able to get production in the Dutch East Indies up to 50 million barrels (~6.8×106 t), 76 percent of its 1940 output rate.[363]
Home fronts and production
In Europe, before the outbreak of the war, the Allies had significant advantages in both population and economics. In 1938, the Western Allies (United Kingdom, France, Poland and British Dominions) had a 30 percent larger population and a 30 percent higher gross domestic product than the European Axis (Germany and Italy); if colonies are included, it then gives the Allies more than a 5:1 advantage in population and nearly 2:1 advantage in GDP.[364] In Asia at the same time, China had roughly six times the population of Japan, but only an 89 percent higher GDP; this is reduced to three times the population and only a 38 percent higher GDP if Japanese colonies are included.[364]
Though the Allies economic and population advantages were largely mitigated during the initial rapid blitzkrieg attacks of Germany and Japan, they became the decisive factor by 1942, after the United States and Soviet Union joined the Allies, as the war largely settled into one of attrition.[365] While the Allies ability to out-produce the Axis is often attributed to the Allies having more access to natural resources, other factors, such as Germany and Japans reluctance to employ women in the labour force,[366] Allied strategic bombing,[367] and Germanys late shift to a war economy[368] contributed significantly. Additionally, neither Germany nor Japan planned to fight a protracted war, and were not equipped to do so.[369] To improve their production, Germany and Japan used millions of slave labourers;[370] Germany used about 12 million people, mostly from Eastern Europe,[341] while Japan used more than 18 million people in Far East Asia.[349][350]
Advances in technology and warfare
Aircraft were used for reconnaissance, as fighters, bombers, and ground-support, and each role was advanced considerably. Innovation included airlift (the capability to quickly move limited high-priority supplies, equipment, and personnel);[371] and of strategic bombing (the bombing of enemy industrial and population centres to destroy the enemys ability to wage war).[372] Anti-aircraft weaponry also advanced, including defences such as radar and surface-to-air artillery, such as the German 88 mm gun. The use of the jet aircraft was pioneered and, though late introduction meant it had little impact, it led to jets becoming standard in air forces worldwide.[373]
Advances were made in nearly every aspect of naval warfare, most notably with aircraft carriers and submarines. Although aeronautical warfare had relatively little success at the start of the war, actions at Taranto, Pearl Harbor, and the Coral Sea established the carrier as the dominant capital ship in place of the battleship.[374][375][376]
In the Atlantic, escort carriers proved to be a vital part of Allied convoys, increasing the effective protection radius and helping to close the Mid-Atlantic gap.[377] Carriers were also more economical than battleships because of the relatively low cost of aircraft[378] and their not requiring to be as heavily armoured.[379] Submarines, which had proved to be an effective weapon during the First World War,[380] were anticipated by all sides to be important in the second. The British focused development on anti-submarine weaponry and tactics, such as sonar and convoys, while Germany focused on improving its offensive capability, with designs such as the Type VII submarine and wolfpack tactics.[381] Gradually, improving Allied technologies such as the Leigh light, hedgehog, squid, and homing torpedoes proved victorious.
Land warfare changed from the static front lines of World War I to increased mobility and combined arms. The tank, which had been used predominantly for infantry support in the First World War, had evolved into the primary weapon.[382] In the late 1930s, tank design was considerably more advanced than it had been during World War I,[383] and advances continued throughout the war with increases in speed, armour and firepower.
At the start of the war, most commanders thought enemy tanks should be met by tanks with superior specifications.[384] This idea was challenged by the poor performance of the relatively light early tank guns against armour, and German doctrine of avoiding tank-versus-tank combat. This, along with Germanys use of combined arms, were among the key elements of their highly successful blitzkrieg tactics across Poland and France.[382] Many means of destroying tanks, including indirect artillery, anti-tank guns (both towed and self-propelled), mines, short-ranged infantry antitank weapons, and other tanks were utilised.[384] Even with large-scale mechanisation, infantry remained the backbone of all forces,[385] and throughout the war, most infantry were equipped similarly to World War I.[386]
The portable machine gun spread, a notable example being the German MG34, and various submachine guns which were suited to close combat in urban and jungle settings.[386] The assault rifle, a late war development incorporating many features of the rifle and submachine gun, became the standard postwar infantry weapon for most armed forces.[387][388]
Most major belligerents attempted to solve the problems of complexity and security involved in using large codebooks for cryptography by designing ciphering machines, the most well known being the German Enigma machine.[389] Development of SIGINT (signals intelligence) and cryptanalysis enabled the countering process of decryption. Notable examples were the Allied decryption of Japanese naval codes[390] and British Ultra, a pioneering method for decoding Enigma benefiting from information given to Britain by the Polish Cipher Bureau, which had been decoding early versions of Enigma before the war.[391] Another aspect of military intelligence was the use of deception, which the Allies used to great effect, such as in operations Mincemeat and Bodyguard.[390][392] Other technological and engineering feats achieved during, or as a result of, the war include the worlds first programmable computers (Z3, Colossus, and ENIAC), guided missiles and modern rockets, the Manhattan Projects development of nuclear weapons, operations research and the development of artificial harbours and oil pipelines under the English Channel.[393]