Pffffft... blame your own bloody country, thank you very much. 
Grant you, it's wiki, but there's loads of stuff out there to verify it, really. Not to mention the 50 gazillion threads that show up every year where people have to repeat it ad nauseum because people keep moaning that it's all the American's fault..
The practice of dressing up in costumes and begging door to door for treats on holidays dates back to the Middle Ages and includes Christmas wassailing. Trick-or-treating resembles the late medieval practice of souling, when poor folk would go door to door on Hallowmas (November 1), receiving food in return for prayers for the dead on All Souls Day (November 2). It originated in Ireland and Britain,[4] although similar practices for the souls of the dead were found as far south as Italy.[6] Shakespeare mentions the practice in his comedy The Two Gentlemen of Verona (1593), when Speed accuses his master of "puling [whimpering or whining] like a beggar at Hallowmas."[7] The custom of wearing costumes and masks at Halloween goes back to Celtic traditions of attempting to copy the evil spirits or placate them, in Scotland for instance where the dead were impersonated by young men with masked, veiled or blackened faces, dressed in white.[Guising at Halloween in Scotland is recorded in 1895, where masqueraders in disguise carrying lanterns made out of scooped out turnips, visit homes to be rewarded with cakes, fruit and money.[5] The practice of Guising at Halloween in North America is first recorded in 1911, where a newspaper in Kingston, Ontario reported children going "guising" around the neighborhood.
Hope you take the time this year to tell all the little "guisers" that you were wrong.... 