World War II

==Impact==
{{Main|Historiography of World War II}}

===Casualties and war crimes===
{{Main|World War II casualties}}
{{Further|War crimes in World War II}}
[[File:World War II Casualties.svg|thumb|upright=1.8|World War&nbsp;II deaths]]

Estimates for the total number of casualties in the war vary, because many deaths went unrecorded.<ref>''Quick Reference Handbook Set, Basic Knowledge and Modern Technology'' (revised) by [[Edward H. Litchfield]], Ph.D 1984 p. 195 {{ISBN?}}</ref> Most suggest that some 60&nbsp;million people died in the war, including about [[Battle casualties of World War II|20 million military personnel]] and 40&nbsp;million civilians.<ref name="WWII: C&C">{{cite web|last=O'Brien |first=Joseph V |title=World War II: Combatants and Casualties (1937–1945) |url=https://web.jjay.cuny.edu/~jobrien/reference/ob62.html |archive-url=https://web.archive.org/web/20101225004221/https://web.jjay.cuny.edu/~jobrien/reference/ob62.html |archive-date=25 December 2010 |work=Obee's History Page |publisher=John Jay College of Criminal Justice |access-date=28 December 2013 |url-status=dead}}</ref><ref>{{cite web|first=Matthew|last=White|title=Source List and Detailed Death Tolls for the Twentieth Century Hemoclysm|url=https://necrometrics.com/20c5m.htm#Second|work=Historical Atlas of the Twentieth Century|publisher=Matthew White's Homepage|access-date=20 April 2007|archive-url=https://web.archive.org/web/20110307141223/https://necrometrics.com/20c5m.htm#Second|archive-date=7 March 2011|url-status=live}}</ref><ref>{{cite web|title=World War II Fatalities|url=https://secondworldwar.co.uk/index.php/fatalities|publisher=secondworldwar.co.uk|access-date=20 April 2007|archive-url=https://web.archive.org/web/20080922185149/https://secondworldwar.co.uk/index.php/fatalities|archive-date=22 September 2008|url-status=live}}</ref>

The Soviet Union alone lost around 27&nbsp;million people during the war,<ref>{{Harvnb|Hosking|2006|p=[{{GBurl|id=CDMVMqDvp4QC|p=242}} 242]}}</ref> including 8.7&nbsp;million military and 19&nbsp;million civilian deaths.<ref name="Ell&Mak 1994">{{Harvnb|Ellman|Maksudov|1994}}.</ref> A quarter of the total people in the Soviet Union were wounded or killed.<ref>{{Harvnb|Smith|1994|p=204}}.</ref> Germany sustained 5.3&nbsp;million military losses, mostly on the Eastern Front and during the final battles in Germany.<ref name="Herf 2003">{{Harvnb|Herf|2003}}.</ref>

An estimated 11<ref>{{cite web|author=Florida Center for Instructional Technology|url=https://fcit.usf.edu/Holocaust/people/victims.htm|title=Victims|work=A Teacher's Guide to the Holocaust|publisher=[[University of South Florida]]|year=2005|access-date=2 February 2008|archive-url=http://arquivo.pt/wayback/20160516094229/https://fcit.usf.edu/Holocaust/people/victims.htm|archive-date=16 May 2016|url-status=live}}</ref> to 17&nbsp;million<ref name=Niewyk45>{{Harvnb|Niewyk|Nicosia|2000|pp=45–52}}.</ref> civilians died as a direct or as an indirect result of Hitler's [[Racial policy of Nazi Germany|racist policies]], including [[mass killing]] of [[the Holocaust|around 6{{nbsp}}million Jews]], along with [[Romani Holocaust|Roma]], [[Persecution of homosexuals in Nazi Germany|homosexuals]], at least 1.9&nbsp;million ethnic [[World War II casualties of Poland|Poles]]<ref>{{Cite journal|url=https://www.nybooks.com/articles/2009/07/16/holocaust-the-ignored-reality/|title=Holocaust: The Ignored Reality|first=Timothy|last=Snyder|journal=The New York Review of Books|access-date=27 August 2017|date=16 July 2009|volume=56 |issue=12 |archive-url=https://web.archive.org/web/20171010063645/https://www.nybooks.com/articles/2009/07/16/holocaust-the-ignored-reality/|archive-date=10 October 2017|url-status=live}}</ref><ref>{{cite web|url=https://www.ushmm.org/wlc/en/article.php?ModuleId=10005473|title=Polish Victims|website=www.ushmm.org|access-date=27 August 2017|archive-url=https://web.archive.org/web/20160507145904/https://www.ushmm.org/wlc/en/article.php?ModuleId=10005473|archive-date=7 May 2016|url-status=live}}</ref> and [[World War II casualties of the Soviet Union|millions of other Slavs]] (including Russians, Ukrainians and Belarusians), and [[Holocaust victims|other ethnic and minority groups]].<ref>{{cite news|url=https://www.bbc.co.uk/tyne/content/articles/2005/01/20/holocaust_memorial_other_victims_feature.shtml|title=Non-Jewish Holocaust Victims : The 5,000,000 others|work=[[BBC]]|date=April 2006|access-date=4 August 2013|archive-url=https://web.archive.org/web/20130303054845/https://www.bbc.co.uk/tyne/content/articles/2005/01/20/holocaust_memorial_other_victims_feature.shtml|archive-date=3 March 2013|url-status=live}}</ref><ref name=Niewyk45 /> Between 1941 and 1945, more than 200,000 ethnic [[Serbs]], along with Roma and Jews, were [[Genocide of Serbs in the Independent State of Croatia|persecuted and murdered]] by the Axis-aligned Croatian [[Ustaše]] in [[Yugoslavia]].<ref>{{Harvnb|Evans|2008|pp=158–160, 234–236}}.</ref> Concurrently, [[Bosniaks|Muslims]] and [[Croats]] were [[Chetnik war crimes in World War II|persecuted and killed]] by Serb nationalist [[Chetniks]],<ref>{{cite book|last=Redžić|first=Enver|title=Bosnia and Herzegovina in the Second World War|year=2005|publisher=Tylor and Francis|location=New York|isbn=978-0-7146-5625-0|page=155|url=https://books.google.com/books?id=pVCx3jerQmYC&pg=PA155|access-date=18 August 2021|archive-date=7 March 2023|archive-url=https://web.archive.org/web/20230307201309/https://books.google.com/books?id=pVCx3jerQmYC&pg=PA155|url-status=live}}</ref> with an estimated 50,000–68,000 victims (of which 41,000 were civilians).<ref name="Geiger">{{cite journal|first=Vladimir|last=Geiger|publisher=Croatian Institute of History|title=Human Losses of the Croats in World War II and the Immediate Post-War Period Caused by the Chetniks (Yugoslav Army in the Fatherand) and the Partisans (People's Liberation Army and the Partisan Detachments of Yugoslavia/Yugoslav Army) and the Communist Authorities: Numerical Indicators |journal=Review of Croatian History |volume=VIII |issue=1 |date=2012 |url=https://hrcak.srce.hr/103223?lang=en|page=117|access-date=25 October 2015|archive-url=https://web.archive.org/web/20151117064114/https://hrcak.srce.hr/103223?lang=en|archive-date=17 November 2015|url-status=live}}</ref> Also, more than 100,000 Poles were massacred by the [[Ukrainian Insurgent Army]] in the [[Massacres of Poles in Volhynia and Eastern Galicia|Volhynia massacres]], between 1943 and 1945.<ref>{{Cite news|url=https://volhyniamassacre.eu/zw2/history/179,The-Effects-of-the-Volhynian-Massacres.html|title=The Effects of the Volhynian Massacres|last=Massacre|first=Volhynia|work=Volhynia Massacre|access-date=9 July 2018|language=en|archive-url=https://web.archive.org/web/20180621015851/https://volhyniamassacre.eu/zw2/history/179,The-Effects-of-the-Volhynian-Massacres.html|archive-date=21 June 2018|url-status=live}}</ref> At the same time, about 10,000–15,000 Ukrainians were killed by the Polish [[Home Army]] and other Polish units, in reprisal attacks.<ref>{{Cite news|url=https://dzieje.pl/aktualnosci/od-rzezi-wolynskiej-do-akcji-wisla-konflikt-polsko-ukrainski-1943-1947|title=Od rzezi wołyńskiej do akcji Wisła. Konflikt polsko-ukraiński 1943–1947|work=dzieje.pl|access-date=10 March 2018|language=pl|archive-url=https://web.archive.org/web/20180624040412/https://dzieje.pl/aktualnosci/od-rzezi-wolynskiej-do-akcji-wisla-konflikt-polsko-ukrainski-1943-1947|archive-date=24 June 2018|url-status=live}}</ref>

[[File:Nanking bodies 1937.jpg|thumb|left|Bodies of Chinese civilians killed by the [[Imperial Japanese Army]] during the [[Nanjing Massacre]] in December 1937]]
In Asia and the Pacific, the number of people killed by Japanese troops remains contested. According to R.J. Rummel, the Japanese killed between 3{{nbsp}}million and more than 10&nbsp;million people, with the most probable case of almost 6,000,000 people.<ref>{{cite web|url=https://www.hawaii.edu/powerkills/SOD.CHAP3.HTM|title=Statistics|last=Rummell|first=R.J.|work=Freedom, Democide, War|publisher=The University of Hawaii System|access-date=25 January 2010|archive-url=https://web.archive.org/web/20100323044733/https://www.hawaii.edu/powerkills/SOD.CHAP3.HTM|archive-date=23 March 2010|url-status=live}}</ref> According to the British historian [[M. R. D. Foot]], civilian deaths are between 10 million and 20 million, whereas Chinese military casualties (killed and wounded) are estimated to be over five million.<ref>{{Harvnb|Dear|Foot|2001|p=182}}.</ref> Other estimates say that up to 30 million people, most of them civilians, were killed.<ref>{{Cite book|last1=Carmichael|first1=Cathie|last2=Maguire|first2=Richard| title=The Routledge History of Genocide|publisher=Routledge|year=2015|page=105|isbn=978-0-367-86706-5}}</ref><ref>{{cite web |url=https://www.historynet.com/a-culture-of-cruelty/ |title=A Culture of Cruelty |publisher=HistoryNet |date=6 November 2017 |access-date=7 May 2022 |archive-date=7 May 2022 |archive-url=https://web.archive.org/web/20220507032834/https://www.historynet.com/a-culture-of-cruelty/ |url-status=live }}</ref> The most infamous Japanese atrocity was the [[Nanjing Massacre]], in which fifty to three hundred thousand Chinese civilians were raped and murdered.<ref>{{Harvnb|Chang|1997|p=102}}.</ref> Mitsuyoshi Himeta reported that 2.7&nbsp;million casualties occurred during the [[Three Alls policy]]. General [[Yasuji Okamura]] implemented the policy in [[Hebei]] and [[Shandong]].<ref>{{Harvnb|Bix|2000|p=?}}.</ref>

Axis forces employed [[Biological warfare|biological]] and [[Chemical warfare|chemical weapons]]. The [[Imperial Japanese Army]] used a variety of such weapons during its [[Second Sino-Japanese War|invasion and occupation of China]] (''see [[Unit 731]]'')<ref>{{Cite book|last=Gold|first=Hal|title=Unit 731 testimony|publisher=Tuttle|year=1996|pages=75–77|isbn=978-0-8048-3565-7}}</ref><ref>{{Harvnb|Tucker|Roberts|2004|p=320}}.</ref> and in [[Battles of Khalkhin Gol|early conflicts against the Soviets]].<ref>{{Harvnb|Harris|2002|p=74}}.</ref> Both the Germans and the [[Japanese human experimentation on the Chinese|Japanese tested]] such weapons against civilians,<ref>{{Harvnb|Lee|2002|p=69}}.</ref> and sometimes on [[prisoner of war|prisoners of war]].<ref>{{cite news|title=Japan tested chemical weapons on Aussie POW: new evidence|newspaper=[[The Japan Times Online]]|date=27 July 2004|url=https://search.japantimes.co.jp/member/nn20040727a9.html|archive-url=https://archive.today/20120529003741/https://search.japantimes.co.jp/member/nn20040727a9.html|url-status=dead|archive-date=29 May 2012|access-date=25 January 2010}}</ref>

The Soviet Union was responsible for the [[Katyn massacre]] of 22,000 Polish officers,<ref>Kużniar-Plota, Małgorzata (30 November 2004). "Decision to commence investigation into Katyn Massacre". Departmental Commission for the Prosecution of Crimes against the Polish Nation. Retrieved 4 August 2011.</ref> and the imprisonment or execution of [[NKVD prisoner massacres|hundreds of thousands of political prisoners]] by the [[NKVD]] secret police, along with [[Population transfer in the Soviet Union|mass civilian deportations to Siberia]], in the [[Occupation of the Baltic states|Baltic states]] and [[Territories of Poland annexed by the Soviet Union|eastern Poland]] annexed by the Red Army.<ref>Robert Gellately (2007).'' Lenin, Stalin, and Hitler: The Age of Social Catastrophe''. Knopf, {{ISBN|978-1-4000-4005-6}} p. 391</ref> Soviet soldiers committed mass rapes in occupied territories, especially [[Soviet occupation zone in Germany|in Germany]].<ref>{{cite book|title=Women and War|url={{GBurl|id=lyZYS_GxglIC|p=480}}|year=2006|publisher=ABC-CLIO|isbn=978-1-85109-770-8|pages=480–}}</ref><ref name=Bird>{{cite journal |last=Bird |first=Nicky |title=Berlin: The Downfall 1945 by Antony Beevor |journal=International Affairs |volume=78 |number=4 |date=October 2002 |pages=914–916 |institution=Royal Institute of International Affairs}}</ref> The exact number of German women and girls raped by Soviet troops during the war and occupation is uncertain, but historians estimate their numbers are likely in the hundreds of thousands, and possibly as many as two million,<ref name=":4">{{Cite book|last=Naimark|first=Norman|title=The Russians in Germany: A History of the Soviet Zone of Occupation, 1945–1949|publisher=Cambridge: Belknap Press|year=1995|isbn=|location=|pages=70}}</ref> while figures for women raped by German soldiers in the Soviet Union go as far as ten million.<ref>[http://www.gegenwind.info/175/sonderheft_wehrmacht.pdf Zur Debatte um die Ausstellung Vernichtungskrieg. Verbrechen der Wehrmacht 1941–1944 im Kieler Landeshaus (Debate on the War of Extermination. Crimes of the Wehrmacht, 1941–1944)] {{Webarchive|url=https://web.archive.org/web/20110718080318/http://www.gegenwind.info/175/sonderheft_wehrmacht.pdf |date=18 July 2011 }} (PDF). Kiel. 1999.</ref><ref>Pascale R . Bos, "Feminists Interpreting the Politics of Wartime Rape: Berlin, 1945"; Yugoslavia, 1992–1993 ''[[Journal of Women in Culture and Society]]'', 2006, vol. 31, no. 4, pp. 996–1025</ref>

The mass bombing of cities in Europe and Asia has often been called a war crime, although no [[Positive law|positive]] or specific [[Customary international law|customary]] [[international humanitarian law]] with respect to [[aerial warfare]] existed before or during World War&nbsp;II.<ref>{{cite book |title=Terror from the Sky: The Bombing of German Cities in World War II |year=2010 |page=167 |publisher=[[Berghahn Books]] |isbn=978-1-84545-844-7}}</ref> The USAAF [[Air raids on Japan|bombed a total of 67 Japanese cities]], killing 393,000 civilians, including the [[atomic bombings of Hiroshima and Nagasaki]], and destroying 65% of built-up areas.<ref>{{cite journal|author=John Dower|title=Lessons from Iwo Jima|journal=Perspectives|year=2007|volume=45|issue=6|pages=54–56|url=https://www.historians.org/publications-and-directories/perspectives-on-history/september-2007/lessons-from-iwo-jima|access-date=17 April 2022|archive-url=https://web.archive.org/web/20110117075824/https://www.historians.org/Perspectives/issues/2007/0709/index.cfm|archive-date=17 January 2011|url-status=live}}</ref>

===Genocide, concentration camps, and slave labour===
{{Main|The Holocaust|Nazi concentration camps|Extermination camp|Forced labour under German rule during World War II|Kidnapping of children by Nazi Germany|Nazi human experimentation|Soviet war crimes#World War II|Japanese war crimes}}
[[File:The Liberation of Bergen-belsen Concentration Camp, April 1945 BU4031.jpg|thumb|[[Schutzstaffel]] (SS) female camp guards removing prisoners' bodies from lorries and carrying them to a mass grave, inside the German [[Bergen-Belsen concentration camp]], 1945]]

[[Nazi Germany]], under the [[dictatorship]] of Adolf Hitler, was responsible for murdering about 6{{nbsp}}million Jews in what is now known as [[the Holocaust]]. They also murdered an additional 4{{nbsp}}million others who were deemed "[[life unworthy of life|unworthy of life]]" (including the [[Disability|disabled]] and [[Mental disorder|mentally ill]], [[German atrocities committed against Soviet prisoners of war|Soviet prisoners of war]], [[Romani people|Romani]], [[homosexuals]], [[Freemasons]], and [[Jehovah's Witnesses]]) as part of a program of deliberate extermination, in effect becoming a "[[Genocide|genocidal]] state".<ref>''The World Must Know: The History of the Holocaust as Told in the United States Holocaust Memorial Museum'' (2nd ed.), 2006. Washington, DC: United States Holocaust Memorial Museum. {{ISBN|978-0-8018-8358-3}}.</ref> [[German atrocities committed against Soviet prisoners of war|Soviet POWs]] were kept in especially unbearable conditions, and 3.6&nbsp;million Soviet POWs out of 5.7&nbsp;million died in Nazi camps during the war.<ref>{{Harvnb|Herbert|1994|p=[{{GBurl|id=M7Y9AAAAIAAJ|p=222}} 222]}}</ref><ref name="Overy 2004 568_569">{{Harvnb|Overy|2004|pp=568–569}}.</ref> In addition to [[Nazi concentration camps|concentration camps]], [[Extermination camp|death camps]] were created in Nazi Germany to exterminate people on an industrial scale. Nazi Germany extensively used [[Forced labour under German rule during World War II|forced labourers]]; about 12&nbsp;million [[Ostarbeiter|Europeans]] from German-occupied countries were abducted and used as a slave work force in German industry, agriculture and war economy.<ref name="compensation">{{cite web|url=https://www.dw-world.de/dw/article/0,2144,1757323,00.html|title=Final Compensation Pending for Former Nazi Forced Laborers|date=27 October 2005|access-date=19 January 2010|first=Michael|last=Marek|archive-url=https://web.archive.org/web/20060502123049/https://www.dw-world.de/dw/article/0,2144,1757323,00.html|archive-date=2 May 2006|work=dw-world.de|publisher=Deutsche Welle|url-status=dead}}</ref>

[[File:Czeslawa Kwoka - Brasse.jpg|thumb|left|[[Czesława Kwoka|Prisoner identity photograph of a Polish girl]] taken by the German [[SS]] in [[Auschwitz]].<ref>{{cite web |url=https://www.dw.com/en/colorized-photo-of-girl-at-auschwitz-strikes-chord-on-social-media/a-43033478 |title=Color photo of girl at Auschwitz strikes chord |first=Alexander |last=Pearson |date=March 19, 2018 |access-date=July 12, 2023 |work=[[Deutsche Welle]] |quote=Kwoka was murdered with a phenol injection to the heart a few weeks later. |archive-date=19 March 2018 |archive-url=https://web.archive.org/web/20180319065203/https://www.dw.com/en/colorized-photo-of-girl-at-auschwitz-strikes-chord-on-social-media/a-43033478 |url-status=live }}</ref> Approximately 230,000 children were held prisoner and used in forced labour and [[Nazi human experimentation|Nazi medical experiments]].]]
The Soviet [[Gulag]] became a ''de facto'' system of deadly camps during 1942–43, when wartime privation and hunger caused numerous deaths of inmates,<ref>J. Arch Getty, Gábor T. Rittersporn and Viktor N. Zemskov. Victims of the Soviet Penal System in the Pre-War Years: A First Approach on the Basisof Archival Evidence. ''The American Historical Review'', Vol. 98, No. 4 (Oct. 1993), pp. 1017–49</ref> including foreign citizens of Poland and [[Occupation of the Baltic states|other countries]] occupied in 1939–40 by the Soviet Union, as well as Axis [[German prisoners of war in the Soviet Union|POWs]].<ref>{{Harvnb|Applebaum|2003|pp=389–396}}.</ref> By the end of the war, most Soviet POWs liberated from Nazi camps and many repatriated civilians were detained in special filtration camps where they were subjected to [[NKVD]] evaluation, and 226,127 were sent to the Gulag as real or perceived Nazi collaborators.<ref>Zemskov V.N. ''On repatriation of Soviet citizens''. Istoriya SSSR., 1990, No. 4, (in Russian). See also [https://scepsis.ru/library/id_1234.html] {{Webarchive|url=https://web.archive.org/web/20111014134645/https://scepsis.ru/library/id_1234.html|date=14 October 2011}} (online version), and {{Harvnb|Bacon|1992}}; {{Harvnb|Ellman|2002}}.</ref>

Japanese [[prisoner-of-war camp]]s, 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 percent (for American POWs, 37 percent),<ref>{{cite web|url=https://www.pbs.org/wgbh/amex/bataan/peopleevents/e_atrocities.html|title=Japanese Atrocities in the Philippines|access-date=18 January 2010|archive-date=27 July 2003|archive-url=https://web.archive.org/web/20030727223501/https://www.pbs.org/wgbh/amex/bataan/peopleevents/e_atrocities.html|work=American Experience: the Bataan Rescue|publisher=PBS Online|url-status=dead}}</ref> seven times that of POWs under the Germans and Italians.<ref>{{Harvnb|Tanaka|1996|pp=2–3}}.</ref> 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.<ref>{{Harvnb|Bix|2000|p=360}}.</ref>

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&nbsp;million.<ref name="zhifen2002">{{cite web|last=Ju|url=https://www.fas.harvard.edu/~asiactr/sino-japanese/session6.htm|first=Zhifen|title=Japan's Atrocities of Conscripting and Abusing North China Draftees after the Outbreak of the Pacific War|work=Joint Study of the Sino-Japanese War: Minutes of the June 2002 Conference|publisher=Harvard University Faculty of Arts and Sciences|date=June 2002|archive-url=https://web.archive.org/web/20120521093637/https://www.fas.harvard.edu/~asiactr/sino-japanese/session6.htm|archive-date=21 May 2012|access-date=28 December 2013}}</ref> In [[Java]], between 4{{nbsp}}and 10&nbsp;million ''[[rōmusha]]'' (Japanese: "manual labourers"), were forced to work by the Japanese military. About 270,000 of these Javanese labourers were sent to other Japanese-held areas in Southeast Asia, and only 52,000 were repatriated to Java.<ref name="indonesiaww2">{{cite web|url=https://lcweb2.loc.gov/cgi-bin/query/r?frd/cstdy:@field(DOCID+id0029)|title=Indonesia: World War II and the Struggle For Independence, 1942–50; The Japanese Occupation, 1942–45|access-date=9 February 2007|publisher=Library of Congress|year=1992|archive-url=https://web.archive.org/web/20041030225658/https://lcweb2.loc.gov/cgi-bin/query/r?frd%2Fcstdy%3A%40field%28DOCID+id0029%29|archive-date=30 October 2004|url-status=live}}</ref>

===Occupation===
{{Main|German-occupied Europe|Resistance during World War II|Collaboration with Nazi Germany and Fascist Italy|Collaboration with Imperial Japan|Nazi plunder}}
[[File:Palmiry before execution.jpg|thumb|Polish civilians wearing blindfolds photographed just before being massacred by German soldiers in [[Palmiry massacre|Palmiry forest]], 1940]]

In Europe, occupation came under two forms. In Western, Northern, and Central Europe (France, Norway, Denmark, the Low Countries, and the [[Protectorate of Bohemia and Moravia|annexed portions of Czechoslovakia]]) Germany established economic policies through which it collected roughly 69.5&nbsp;billion reichsmarks (27.8&nbsp;billion U.S. dollars) by the end of the war; this figure does not include the [[Nazi plunder|plunder]] of industrial products, military equipment, raw materials and other goods.<ref>{{Harvnb|Liberman|1996|p=42}}.</ref> 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.<ref name="Milward 1979 138">{{Harvnb|Milward|1992|p=138}}.</ref>

[[File:Bundesarchiv Bild 101I-031-2436-03A, Russland, Hinrichtung von Partisanen retouched.jpg|thumb|left|[[Soviet partisans]] hanged by the German army. The [[Russian Academy of Sciences]] reported in 1995 that [[World War II casualties of the Soviet Union|civilian victims in the Soviet Union]] at German hands totalled 13.7 million dead, twenty percent of the 68 million people in the occupied Soviet Union.]]

In the East, the intended gains of ''[[Lebensraum]]'' were never attained as fluctuating front-lines and Soviet [[scorched earth]] policies denied resources to the German invaders.<ref name="Milward 1992 148">{{Harvnb|Milward|1992|p=148}}.</ref> Unlike in the West, the [[Racial policy of Nazi Germany|Nazi racial policy]] encouraged extreme brutality against what it considered to be the "[[Untermensch|inferior people]]" of Slavic descent; most German advances were thus followed by [[Generalplan Ost|mass atrocities and war crimes]].<ref>{{Harvnb|Barber|Harrison|2006|p=232}}.</ref> The Nazis [[Nazi crimes against the Polish nation|killed an estimated 2.77&nbsp;million ethnic Poles]] during the war in addition to Polish-Jewish victims of the Holocaust.<ref>Institute of National Remembrance, Polska 1939–1945 Straty osobowe i ofiary represji pod dwiema okupacjami. Materski and Szarota. p. 9 ''"Total Polish population losses under German occupation are currently calculated at about 2 770 000"''.</ref>{{better source needed|date=July 2023}} Although [[Resistance during World War II|resistance groups]] formed in most occupied territories, they did not significantly hamper German operations in either the East<ref>{{Harvnb|Hill|2005|p=5}}.</ref> or the West<ref>{{Harvnb|Christofferson|Christofferson|2006|p=156}}</ref> 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.<ref>{{Harvnb|Radtke|1997|p=107}}.</ref> Although Japanese forces were sometimes welcomed as liberators from European domination, [[Japanese war crimes]] frequently turned local public opinion against them.<ref name="GSWW6_266">{{Harvnb|Rahn|2001|p=266}}.</ref> During Japan's initial conquest, it captured {{convert|4000000|oilbbl}} of oil (~550,000 tonnes) left behind by retreating Allied forces; and by 1943, was able to get production in the Dutch East Indies up to {{convert|50|e6oilbbl}} of oil (~6.8 million tonnes), 76 percent of its 1940 output rate.<ref name="GSWW6_266" />

===Home fronts and production===
{{Main|Military production during World War II|Home front during World War II}}
{{Image frame
 | caption=Allies to Axis GDP ratio between 1938 and 1945
 | content = {{Graph:Chart
 | width = 275
 | height = 200
 | type = line
 | xAxisTitle = Year
 | yAxisTitle = Allies GDP / Axis GDP
 | yAxisFormat = %
 | yAxisMin = 0.00
 | x = 1938,1939,1940,1941,1942,1943,1944,1945
 | y = 2.38,2.15,1.58,1.75,2.06,2.31,2.86,5.02
}}
}}

In the 1930s Britain and the United States of America together controlled almost 75% of world mineral output - essential for projecting military power.<ref>{{cite journal
 |last1            = Leith
 |first1           = C. K.
 |author-link1     = Charles Kenneth Leith
 |title            = The Struggle for Mineral Resources
 |url              = http://www.jstor.org/stable/1021443
 |journal          = The Annals of the American Academy of Political and Social Science
 |publication-date = July 1939
 |volume           = 204, Democracy and the Americas
 |pages            = 42–48
 |jstor            = 1021443
 |quote            = [...] mineral raw materials [...] are the basis of industrial power, and this in turn is the basis of military power. [...] England and the United States of America alone control economic proportions of nearly three-fourths of the world's production of minerals. Not less important, they control the seas over which the products must pass.
 |access-date      = 26 January 2024
 |archive-date     = 26 January 2024
 |archive-url      = https://web.archive.org/web/20240126024338/https://www.jstor.org/stable/1021443
 |url-status       = live
}}</ref>

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 the British Dominions) had a 30 percent larger population and a 30 percent higher gross domestic product than the European Axis powers (Germany and Italy); including colonies, the Allies had more than a 5:1 advantage in population and a nearly 2:1 advantage in GDP.<ref name="6Econ3">{{Harvnb|Harrison|1998|p= 3}}.</ref> In Asia at the same time, China had roughly six times the population of Japan but only an 89 percent higher GDP; this reduces to three times the population and only a 38 percent higher GDP if Japanese colonies are included.<ref name="6Econ3" />

The United States produced about two-thirds of all munitions used by the Allies in World War II, including warships, transports, warplanes, artillery, tanks, trucks, and ammunition.<ref>Compare:
{{cite book |last1 = Wilson |first1 = Mark R. |title = Destructive Creation: American Business and the Winning of World War II |url = https://books.google.com/books?id=AcqADAAAQBAJ |series = American Business, Politics, and Society |edition = reprint |location = Philadelphia |publisher = University of Pennsylvania Press |date = 2016 |page = 2 |isbn = 978-0-8122-9354-8 |access-date = 19 December 2019 |quote = By producing nearly two thirds of the munitions used by Allied forces – including huge numbers of aircraft, ships, tanks, trucks, rifles, artillery shells, and bombs – American industry became what President Franklin D. Roosevelt once called 'the arsenal of democracy' [...].|archive-date = 7 March 2023|archive-url = https://web.archive.org/web/20230307201318/https://books.google.com/books?id=AcqADAAAQBAJ|url-status = live}}</ref>
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 and the war evolved into one of [[Attrition warfare|attrition]].<ref name="6Econ2">{{Harvnb|Harrison|1998|p=2}}.</ref> While the Allies' ability to out-produce the Axis was partly due to more access to natural resources, other factors, such as Germany and Japan's reluctance to employ women in the [[Workforce |labour force]],<ref>{{Harvnb|Bernstein|1991|p= 267}}.</ref> Allied [[Strategic bombing during World War II|strategic bombing]],<ref>{{Cite book |last= Griffith |first= Charles |title= The Quest: Haywood Hansell and American Strategic Bombing in World War II|isbn= 978-1-58566-069-8|publisher= Diane Publishing|year= 1999 |page= 203}}</ref> and Germany's late shift to a [[war economy]]<ref>{{Harvnb|Overy|1994|p= 26}}.</ref> contributed significantly. Additionally, neither Germany nor Japan planned to fight a protracted war, and had not equipped themselves to do so.<ref>{{Harvnb|BBSU|1998|p= 84}}; {{Harvnb|Lindberg|Todd|2001|p= 126}}.</ref> To improve their production, Germany and Japan used millions of [[Slavery |slave labourers]];<ref>{{Cite book |last= Unidas |first= Naciones |title= World Economic And Social Survey 2004: International Migration |page= 23 |publisher= United Nations Pubns |year= 2005 |isbn= 978-92-1-109147-2}}</ref> [[Forced labour under German rule during World War II|Germany enslaved]] about 12&nbsp;million people, mostly from Eastern Europe,<ref name="compensation" /> while [[Slavery in Japan|Japan used]] more than 18&nbsp;million people in Far East Asia.<ref name="zhifen2002" /><ref name="indonesiaww2" />

===Advances in technology and its application===
{{Main|Technology during World War II}}
[[File:Bundesarchiv Bild 146-1978-Anh.026-01, Peenemünde, V2 beim Start.jpg|thumb|A [[V-2 rocket]] launched from a fixed site in [[Peenemünde]], 21 June 1943]]

Aircraft were used for [[Reconnaissance aircraft|reconnaissance]], as [[fighter aircraft|fighters]], [[bomber]]s, and [[close air support|ground-support]], and each role developed considerably. Innovations included [[airlift]] (the capability to quickly move limited high-priority supplies, equipment, and personnel);<ref name="EncWWII_76">{{Harvnb|Tucker|Roberts|2004|p=76}}.</ref> and [[strategic bombing]] (the bombing of enemy industrial and population centres to destroy the enemy's ability to wage war).<ref>{{Harvnb|Levine|1992|p=227}}.</ref> [[Anti-aircraft warfare|Anti-aircraft weaponry]] also advanced, including defences such as [[radar]] and surface-to-air artillery, in particular the introduction of the [[proximity fuze]]. The use of the [[jet aircraft]] was pioneered and led to jets becoming standard in air forces worldwide.<ref>{{Harvnb|Klavans|Di Benedetto|Prudom|1997}}; {{Harvnb|Ward|2010|pp=247–251}}.</ref>

Advances were made in nearly every aspect of [[naval warfare]], most notably with [[aircraft carrier]]s and [[submarine]]s. Although [[Aeronautics|aeronautical]] warfare had relatively little success at the start of the war, [[Battle of Taranto|actions at Taranto]], [[Attack on Pearl Harbor|Pearl Harbor]], and the [[Battle of the Coral Sea|Coral Sea]] established the carrier as the dominant capital ship (in place of the battleship).<ref name="EncWWII_163">{{Harvnb|Tucker|Roberts|2004|p=163}}.</ref><ref>{{Cite book|last1= Bishop|first1= Chris|last2= Chant|first2=Chris|title=Aircraft Carriers: The World's Greatest Naval Vessels and Their Aircraft|page= 7|publisher= Silverdale Books|year= 2004|isbn=978-1-84509-079-1|location= Wigston, Leics}}</ref><ref>{{Cite book|last1=Chenoweth|first1=H. Avery|last2= Nihart|first2= Brooke|title= Semper Fi: The Definitive Illustrated History of the U.S. Marines|publisher= Main Street|year= 2005|isbn= 978-1-4027-3099-3|page= 180|location= New York}}</ref> In the Atlantic, [[escort carrier]]s became a vital part of Allied convoys, increasing the effective protection radius and helping to close the [[Mid-Atlantic gap]].<ref>{{Harvnb|Sumner|Baker|2001|p=25}}.</ref> Carriers were also more economical than [[battleship]]s due to the relatively low cost of aircraft<ref>{{Harvnb|Hearn|2007|p=14}}.</ref> and because they are not required to be as heavily armoured.<ref>{{Harvnb|Gardiner|Brown|2004|p=52}}.</ref> Submarines, which had proved to be an effective weapon during the [[World War I|First World War]],<ref name="Bur&Ryd 1995 15">{{Harvnb|Burcher|Rydill|1995|p=15}}.</ref> were expected by all combatants to be important in the second. The British focused development on [[Anti-submarine warfare|anti-submarine]] [[anti-submarine weapon|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 (naval tactic)|wolfpack]] tactics.<ref name="Bur&Ryd 1995 16">{{Harvnb|Burcher|Rydill|1995|p=16}}.</ref>{{Better source needed|reason=this is arguably a reference in passing – the book is about the design of submarines and deals with this fairly superficially. Also reference in article only points to a review of this book.|date=July 2020}} Gradually, improving Allied technologies such as the [[Leigh Light]], [[Hedgehog (weapon)|Hedgehog]], [[Squid (weapon)|Squid]], and [[Mark 24 mine|homing torpedoes]] proved effective against German submarines.<ref>{{Cite journal |title= Impact of technology on the defeat of the U-boat September 1939 – May 1943 |journal=  IEE Proceedings - Science, Measurement and Technology|date=September 1994 |volume=141 |issue=5 |pages=343–355 |doi=10.1049/ip-smt:19949918 |last1=Burns |first1=R. W. }}</ref>

[[File:Trinity device readied.jpg|thumb|Nuclear ''Gadget'' being raised to the top of the detonation "shot tower", at [[Alamogordo Bombing and Gunnery Range|Alamogordo Bombing Range]]; [[Trinity (nuclear test)|Trinity nuclear test]], [[New Mexico]], July 1945]]
[[Land warfare]] changed from the static frontlines of [[trench warfare]] of World War&nbsp;I, which had relied on improved [[artillery]] that outmatched the speed of both [[infantry]] and [[cavalry]], 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.<ref name="EncWWII_125">{{Harvnb|Tucker|Roberts|2004|p=125}}.</ref> In the late 1930s, tank design was considerably more advanced than it had been during World War{{nbsp}}I,<ref>{{Cite book|last= Dupuy|first= Trevor Nevitt|title= The Evolution of Weapons and Warfare|publisher=[[Jane's Information Group]]|isbn= 978-0-7106-0123-0|year= 1982|page= 231}}</ref> and [[Tanks in World War II|advances continued throughout the war]] with increases in speed, armour and firepower.<ref>{{cite web |title=The Vital Role Of Tanks In The Second World War |url= https://www.iwm.org.uk/history/the-vital-role-of-tanks-in-the-second-world-war |access-date=5 April 2022 |website=Imperial War Museums |language=en |archive-date=25 March 2022 |archive-url=https://web.archive.org/web/20220325104344/https://www.iwm.org.uk/history/the-vital-role-of-tanks-in-the-second-world-war |url-status=live }}</ref><ref>{{Cite journal |last1=Castaldi |first1=Carolina |last2=Fontana |first2=Roberto |last3=Nuvolari |first3=Alessandro |date=1 August 2009 |title='Chariots of fire': the evolution of tank technology, 1915–1945 |journal=Journal of Evolutionary Economics |language=en |volume=19 |issue=4 |pages=545–566 |doi=10.1007/s00191-009-0141-0 |s2cid=36789517 |issn=1432-1386 |doi-access=free |hdl=10419/89322 |hdl-access=free }}</ref> At the start of the war, most commanders thought enemy tanks should be met by tanks with superior specifications.<ref name="EncWWII_108">{{Harvnb|Tucker|Roberts|2004|p=108}}.</ref> 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 Germany's use of combined arms, were among the key elements of their highly successful blitzkrieg tactics across Poland and France.<ref name="EncWWII_125" /> Many means of [[Anti-tank warfare|destroying tanks]], including [[Indirect fire|indirect artillery]], [[anti-tank gun]]s (both towed and [[Self-propelled artillery|self-propelled]]), [[Anti-tank mine|mines]], short-ranged infantry antitank weapons, and other tanks were used.<ref name="EncWWII_108" /> Even with large-scale mechanisation, infantry remained the backbone of all forces,<ref name="EncWWII_734">{{Harvnb|Tucker|Roberts|2004|p=734}}.</ref> and throughout the war, most infantry were equipped similarly to World War&nbsp;I.<ref name="Comp_221">{{Harvnb|Cowley|Parker|2001|p=221}}.</ref> The portable machine gun spread, a notable example being the German [[MG 34]], and various [[submachine gun]]s which were suited to [[close combat]] in urban and jungle settings.<ref name="Comp_221" /> The [[assault rifle]], a late war development incorporating many features of the rifle and submachine gun, became the standard post-war infantry weapon for most armed forces.<ref>{{cite web |title=The AK-47: the worlds favourite killing machine |publisher=controlarms.org |first1=Oliver |last1=Sprague |first2=Hugh |last2=Griffiths |url=https://www.amnesty.org/en/documents/act30/011/2006/en/ |access-date=14 November 2009 |year=2006 |format=PDF |page=1 |archive-url=https://web.archive.org/web/20181228130914/https://www.amnesty.org/en/documents/act30/011/2006/en/ |archive-date=28 December 2018 |url-status=live}}</ref>

Most major belligerents attempted to solve the problems of complexity and security involved in using large [[codebook]]s for [[cryptography]] by designing [[cipher]]ing machines, the most well-known being the German [[Enigma machine]].<ref>{{Harvnb|Ratcliff|2006|p=11}}.</ref> Development of [[SIGINT]] (''sig''nals ''int''elligence) and [[cryptanalysis]] enabled the countering process of decryption. Notable examples were the Allied decryption of [[Japanese naval codes]]<ref name=Schoenherr>{{cite web|access-date=15 November 2009|archive-date=9 May 2008|archive-url=https://web.archive.org/web/20080509054959/https://history.sandiego.edu/gen/WW2Timeline/espionage.htm|first=Steven|last=Schoenherr|publisher=History Department at the University of San Diego|title=Code Breaking in World War I|url=https://history.sandiego.edu/gen/WW2Timeline/espionage.htm|url-status=dead|year=2007}}</ref> and British [[Ultra (cryptography)|Ultra]], a [[Bombe#The British Bombe|pioneering method]] for decoding Enigma that benefited from information given to the United Kingdom by the [[Cipher Bureau (Poland)#Gift to allies|Polish Cipher Bureau]], which had been decoding early versions of Enigma before the war.<ref>{{cite news |author=Macintyre, Ben |date=10 December 2010 |title=Bravery of thousands of Poles was vital in securing victory |page=27 |work=The Times |location=London |id={{Gale|IF0504159516}}}}</ref> Another component of [[military intelligence]] was [[deception]], which the Allies used to great effect in operations such as [[Operation Mincemeat|Mincemeat]] and [[Operation Bodyguard|Bodyguard]].<ref name=Schoenherr /><ref>{{cite web|title=Deception for Defense of Information Systems: Analogies from Conventional Warfare|url=https://www.au.af.mil/au/awc/awcgate/nps/mildec.htm|first1=Neil C.|last1=Rowe|first2=Hy|last2=Rothstein|work=Departments of Computer Science and Defense Analysis U.S. Naval Postgraduate School|publisher=Air University|access-date=15 November 2009|archive-url=https://web.archive.org/web/20101123031630/https://www.au.af.mil/au/awc/awcgate/nps/mildec.htm|archive-date=23 November 2010|url-status=live}}</ref>

Other technological and engineering feats achieved during, or as a result of, the war include the world's first programmable computers ([[Z3 (computer)|Z3]], [[Colossus computer|Colossus]], and [[ENIAC]]), [[V-1 flying bomb|guided missiles]] and [[V-2 rocket|modern rockets]], the [[Manhattan Project]]'s development of [[nuclear weapon]]s, [[operations research]], the development of [[Mulberry harbour|artificial harbours]], and [[Operation Pluto|oil pipelines under the English Channel]].<ref>{{Cite web |title=World War – II |url=https://www.insightsonindia.com/world-history/world-war-i/world-war-ii/ |website=InsightsIAS |language=en-US |access-date=17 September 2022 |archive-date=11 July 2022 |archive-url=https://web.archive.org/web/20220711080947/https://www.insightsonindia.com/world-history/world-war-i/world-war-ii/ |url-status=live }}</ref> [[Penicillin]] was first [[History of penicillin|developed, mass-produced, and used]] during the war.<ref>{{cite web|archive-url= https://web.archive.org/web/20190628035235/https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/flemingpenicillin.html|archive-date=28 June 2019|url= https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/flemingpenicillin.html |title=Discovery and Development of Penicillin: International Historic Chemical Landmark|location=Washington, DC|publisher=[[American Chemical Society]]|access-date=15 July 2019}}</ref>