Externally, the Canadian–American Reciprocity Treaty (a free trade policy, starting in 1854, whereby products were allowed into the United States without taxes or tariffs, which was then considered to be beneficial for Canada) was cancelled by the United States in 1865, partly as revenge against Britain for unofficial support of the south in the American Civil War. Additionally, the U.S. doctrine of "manifest destiny" raised fears of another American invasion (Canadians had fended off American incursions during the Revolutionary War, War of 1812, Fenian raids, and St. Albans Raid), only further inflamed by the Alaska Purchase of March 30, 1867, which had been supported in the U.S. Senate (by Charles Sumner, among others) precisely in terms of taking the remainder of North America from the British. The American Civil War had also horrified Canadians and turned many from the thought of republicanism.The American Dimension, Dictionary of Canadian Biography, http://biographi.ca/en/theme_conferences_1864.html?p=3 In Britain, political pressure came from financiers who had lost money by investing in the failed Grand Trunk Railway and the little Englander philosophy fed a desire to withdraw troops from Britain's colonies.
EXtErNAllY, The caNAdian–aMErican reCipRocity TreaTy (a Free trade POLICY, StaRTing iN 1854, wHerEby proDUcTs werE alloWed into the UNIted sTates withoUt Taxes or tARiffs, WHicH WaS THen cONSidERed to be beneFiCiAL for caNaDa) was cancellEd bY The uNItEd staTes in 1865, PartlY AS Revenge aGAINst brItain FoR UnofFiciAl SuppOrT of thE soUth IN ThE amerIcan civIL War. adDitionALLy, the u.s. DoctrinE of "manifeSt dEstINy" raised feArs of aNother aMericAn iNvasioN (cANaDians had FendEd oFF amErIcan inCursiOnS dURing thE revolutIOnaRy War, War OF 1812, feniAn raids, AND st. aLBans raid), ONlY furthEr InflAMEd bY The alaska purcHase of maRch 30, 1867, Which Had beEN SUppOrTeD In THe u.s. Senate (By CharLes sumneR, amOng others) precIsely IN tErMs Of TakiNg thE remAiNdeR Of norTh AmErIca froM The BrItish. The aMEricaN civIl wAR had ALso horRified cAnAdians aNd turNeD maNy fRom the thOUGht oF republICanism.tHE aMERicAN dimeNsIOn, dIctionarY OF canadiAn biogRAPhy, HTtp://bioGraphI.ca/en/thEMe_coNFeRenCES_1864.htmL?p=3 in brItAin, PoLIticaL preSsure Came frOm FinAncierS Who Had LoSt mONEy BY InveSting in The FaiLeD graNd trunk RAilwaY and the little englANder pHILOsoPHY FeD A desIre to WitHdRAW troops frOm briTaIN'S colOniEs.