WhatpromptedLopeztoembarkonhiscareerofinternationalmadnessandprosecuteitwiththerageofademonisnotentirelyclear。AvisionofhimselfastheNapoleonofsouthernSouthAmerica，whomightcauseBrazil，Argentina，andUruguaytocringebeforehisfootstool，whilehedisposedatwilloftheirterritoryandfortunes，doubtlessstirredhisimagination。So，too，thethoughtofhiscountry，wedgedinbetweentwohugeneighborsandthreatenedwithsuffocationbetweentheiroverlappingfolds，maywellhavesuggestedthewisdomofconqueringoverlandahighwaytothesea。Atallevents，heassembledanarmyofupwardsofninetythousandmen，thegreatestmilitaryarraythatHispanicAmericahadeverseen。Thoughadmirablydrilledanddisciplined，theywerepoorlyarmed，mostlywithflintlockmuskets，andtheywerealsodeficientinartilleryexceptthatofantiquatedpattern。Withthismightyforceathisback，yetknowingthattheneighboringcountriescouldeventuallycallintothefieldarmiesmuchlargerinsizeequippedwithrepeatingriflesandsuppliedwithmodernartillery，the\"JupiterofParaguay\"neverthelessmadereadytolaunchhisthunderbolt。
TheprimaryobjectatwhichheaimedwasUruguay。InthislittlestatetheColorados，upheldopenlyorsecretlybyBrazilandArgentina，wereconductinga\"crusadeofliberty\"againsttheBlancogovernmentatMontevideo，whichwasfavoredbyParaguay。
NeitherofthetwogreatpowerswishedtoseeanallianceformedbetweenUruguayandParaguay，lestwhenunitedinthismannerthesmallernationsmightbecometoostrongtotoleratefurtherinterventionintheiraffairs。Forherpart，BrazilhadmotivesforresentmentarisingoutofboundarydisputeswithParaguayandUruguay，aswellasoutoftheinevitableinjurytoitsnationalsinflictedbythecommotionsinthelattercountry;whereasArgentinacherishedgrievancesagainstLopezfortheaudacitywithwhichhistroopsroamedthroughherprovincesandtheimpudencewithwhichhisvessels，plyingonthelowerParana，ignoredthecustomsregulations。ThusithappenedthatobscurecivildiscordsinonelittlerepublicexplodedintoaterrificinternationalstrugglewhichshookSouthAmericatoitsfoundations。
In1864，scorningtheartsofdiplomacywhichhedidnotapparentlyunderstand，LopezsentdownanorderforthetwobigstatestoleavethematterofUruguayanpoliticstohisimpartialadjustment。AtbothRiodeJaneiroandBuenosAiresaroaroflaughterwentupfromthepressatthisnotionofanobscurechieftainofabandofIndiansinthetropicalbackwoodsdaringtopoisetheequilibriumofmuchmorethanhalfacontinentonhisinsolenthand。Butthemerrimentsoonsubsided，asBraziliansandArgentinoscametorealizewhattheirperilmightbefromahugearmyofskilledandvaliantsoldiers，averitablehordeoffightingfanatics，drawnupinacompactlittleland，centrallylocatedandaffordinginotherrespectseverykindofstrategicadvantage。
WhenBrazilinvadedUruguayandrestoredtheColoradostopower，LopezdemandedpermissionfromArgentinatocrossitsfrontier，forthepurposeofassailinghisenemyfromanotherquarter。Whenthepermissionwasdenied，LopezdeclaredwaronArgentinaalso。