Ⅰ:BecominganimperialpowerWiththerapiddevelopmentofindustry,imperialismemergedinAmerica.Inordertomeetthedevelopmentofindustry,Americanmadesomemadpoliciesofaggressionandexpansionabroad.In1898,Americanlaunchedthefirstimperialistwar,theUS-Spanishwar.Finally,thewarendedupwiththevictoryoftheUS.TheUS-SpanishhadgreatinfluenceonAmerica.Firstly,thewarmarkedanewstageinwhichtheUStransformedintoanimperialistpower.Secondly,thewarisasymbolofthebeginningoftheUSmodernsociety.Thirdly,theUSgotcontrolofPuertoRico,Guam,andthePhilippines.AndCubabecameindependent,butstillundercontrolofAmerica.Atthebeginningof20thcentury,theUSpromotedtocarryoutitsaggressivepolicies.In1901,TheodoreRooseveltwaselectedaspresident.Duringhisadministration,heproposedmanyaggressivepolicies.InLatinAmerica,inthenameof“MonroeDoctrine”,hecarriedout“BigStick”.Consequently,mostoftheCaribbeancountrieswereundercontrolofAmerica.inSino-Americanrelations,hepushedthe“OpenDoorPolicy”whichdemandedthatalltheimperialistpowersshouldenjoyequalchanceinChinaasfreelyasotheraggressors.ThetypicalexampleofhowthispolicyworkedisthatAmericajoinedtheEight-PowerAlliancetosuppresstheanti-imperialistBoxerMovementoftheChinesepeople.Intheendof20thcentury,theUShadbeenconceivedasamajorpowerintheworldaffaires.Thereafter,itbecameafullytrustimperialistcountry.Ⅱ.TagFromthecivilwartothebeginningofthe20thcentury,Americanindustrygrowsrapidly.Atthesametime,Americaneconomicdoctrinetransmittedfromlaissezfairetomonopolycapitalism,alsocalledimperialism.TheformofAmericanmonopolycapitalismiscalledBigTrusts.Atthebeginningof20thcentury,everyimportantindustrialdepartmentwascontrolledbyBigTrusts.AndAmericangrewintoafull-fledgedimperialpower.Inordertoachievethegoalofcapitalexports,Americanmademanyaggressiveforeignpoliciesandlaunchedmanyaggressivewarsabroad.EspeciallyduringtheruleofpresidentTheodoreRoosevelt.InLatinAmerica,inthenameof“MonroeDoctrine”,hecameupwithapolicynamed“BigStick”.Inthisway,hegotcontrolofmanycountriesofLatinAmerica.InChina,hecarriedout“OpenDoorPolicy”.AndthispolicyensuredthatAmericahadthesamerighttooccupychinaastheothercountries.Thoseaggressivediplomaticpoliciesandwarsdidgreatinfluenceonbothhomelandandabroad.Asforhomeland,ononehand,therapiddevelopmentofimperialismmadeworkingclasspeople'slivingconditiongettingworseandworse.What'smore,thepolarizationofAmericawasexacerbated.Theupperclassgotricherandricher,onthecontrary,theworkingclassgotpoorerandpoorersotheworkingclassunsatisfiedwiththeircondition,andtheyheldthebeliefthattheirincomeswerenotinproportionwiththeirpays.Asaresult,theylaunchedmanymovementstoresistandfightfortheirrights.Ontheotherhand,Americatrulygainedlotsofbenefitsfromthat,andlaidfoundationforfurtheringthedevelopmentofeconomy.Inabroad,inordertorealizethedumpingofgoodsandplunderofrawmaterialsandgainmoreprofits,Americanactivelyunfoldedoverseasexpansionandintrudedmanycountries.Inconsequence,peopleinthecountrieswhichwereinvadedbyAmericawereinadesperatelyhardposition.Tosumup,theaggressivepoliciesandintrudingwarsaffectedAmericainmanyways.ImperialismstillworksinAmerica.Inrecentyears,basedonimperialism,Americanworkedout“NewImperialism”togoonwiththeintentionofrulingtheworld.