ABriefIntroductionTheUnitedStatesofAmerica(commonlyreferredtoastheUnitedStates,theU.S.,theUSA,orAmerica)isafederalconstitutionalrepubliccomprisingfiftystatesandafederaldistrict.ThecountryissituatedmostlyincentralNorthAmerica,whereitsforty-eightcontiguousstatesandWashington,D.C.,thecapitaldistrict,liebetweenthePacificandAtlanticOceans,borderedbyCanadatothenorthandMexicotothesouth.ThestateofAlaskaisinthenorthwestofthecontinent,withCanadatoitseastandRussiatothewestacrosstheBeringStrait.ThestateofHawaiiisanarchipelago(群岛)inthemid-Pacific.Thecountryalsopossessesseveralterritories,orinsular(海岛的)areas,scatteredaroundtheCaribbeanandPacific.ABriefIntroductionAt3.79millionsquaremiles(9.83millionkm²)andwithabout305millionpeople,theUnitedStatesisthethirdorfourthlargestcountrybytotalarea,andthirdlargestbylandareaandbypopulation.TheUnitedStatesisoneoftheworld'smostethnicallydiverseandmulticulturalnations,theproductoflarge-scaleimmigrationfrommanycountries.TheU.S.economyisthelargestnationaleconomyintheworld,withanestimated2008grossdomesticproduct(GDP)ofUS$14.3trillion(23%oftheworldtotalbasedonnominalGDPandalmost21%atpurchasingpowerparity).ABriefIntroductionThenationwasfoundedbythirteencoloniesofGreatBritainlocatedalongtheAtlanticseaboard.OnJuly4,1776,theyissuedtheDeclarationofIndependence,whichproclaimedtheirindependencefromGreatBritainandtheirformationofacooperativeunion.TherebelliousstatesdefeatedGreatBritainintheAmericanRevolutionaryWar,thefirstsuccessfulcolonialwarofindependence.AfederalconventionadoptedthecurrentUnitedStatesConstitutiononSeptember17,1787;itsratificationthefollowingyearmadethestatespartofasinglerepublicwithastrongcentralgovernment.TheBillofRights,comprisingtenconstitutionalamendmentsguaranteeingmanyfundamentalcivilrightsandfreedoms,wasratifiedin1791.ABriefIntroductionInthe19thcentury,theUnitedStatesacquiredlandfromFrance,Spain,theUnitedKingdom,Mexico,andRussia,andannexedtheRepublicofTexasandtheRepublicofHawaii.DisputesbetweentheagrarianSouthandindustrialNorthoverstates'rightsandtheexpansionoftheinstitutionofslaveryprovokedtheAmericanCivilWarofthe1860s.TheNorth'svictorypreventedapermanentsplitofthecountryandledtotheendoflegalslaveryintheUnitedStates.Bythe1870s,thenationaleconomywastheworld'slargest.TheSpanish–AmericanWarandWorldWarIconfirmedthecountry'sstatusasamilitarypower.In1945,theUnitedStatesemergedfromWorldWarIIasthefirstcountrywithnuclearweapons,apermanentmemberoftheUnitedNationsSecurityCouncil,andafoundingmemberofNATO.TheendoftheColdWarlefttheUnitedStatesasthesolesuperpower.Thecountryaccountsforapproximately50%ofglobalmilitaryspendingandisaleadingeconomic,political,andculturalforceintheworld.TheRockiesTheRockies,thebackboneoftheNorthAmericanContinent,isalsoknownastheContinentalDivide.TheAppalachianmountainsTheAppalachianmountainsarelocallyknownbydifferentnames:theGreenmountainsandthewhitemountainsinNewEngland,theCatskillsinNewYork,theAllegheniesalongtheeasternseaboard,theCumberlandsinKentucky,theBlueRidgemountainsinVirginia,theGreatSmokiesontheTennessee-NorthCarolinaborderTheMississippiTheMississippiflows3770km(2340mi)fromitssourceatLakeItascainnorthernMinnesotatoitsmouthintheGulfofMexico.WhiletheMississippiranksasthesecondlongestriverintheUnitedStatesaftertheMissouriRiver,itcarriesagreatervolumeofwaterthananyotherAmericanriver.Thismap,illustratingth...
