WorldWarII,ortheSecondWorldWar,[1](oftenabbreviatedWWII)wasaglobalmilitaryconflictwhichinvolvedamajorityoftheworld'snations,includingallofthegreatpowers,[2]organizedintotwoopposingmilitaryalliances:theAlliesandtheAxis.Thewarinvolvedthemobilizationofover100millionmilitarypersonnel,makingitthemostwidespreadwarinhistory.Inastateof"totalwar",themajorparticipantsplacedtheircompleteeconomic,industrial,andscientificcapabilitiesattheserviceofthewareffort,erasingthedistinctionbetweencivilianandmilitaryresources.Over70millionpeople,themajorityofthemcivilians,werekilled,makingitthedeadliestconflictinhumanhistory.[3]

　　ThestartingdateofthewarisgenerallyheldtobeSeptember1939withtheGermaninvasionofPolandandsubsequentdeclarationsofwaronGermanybytheUnitedKingdom,FranceandtheBritishDominions.[4][5]However,asaresultofotherevents,manybelligerentsenteredthewarbeforeorafterthisdate,duringaperiodwhichspannedfrom1937to1941.AmongstthesemaineventsaretheMarcoPoloBridgeIncident,thestartofOperationBarbarossaandtheattackonPearlHarborandBritishandNetherlandscoloniesinSouthEastAsia.

　　TheSovietUnionandtheUnitedStatesemergedfromthewarastheworld'sleadingsuperpowers.ThissetthestagefortheColdWar,whichlastedforthenext45years.TheUnitedNationswasformedinthehopeofpreventinganothersuchconflict.TheselfdeterminationspawnedbythewaraccelerateddecolonizationmovementsinAsiaandAfrica,whileWesternEuropeitselfbeganmovingtowardintegration.