The whole damn holdiay started in Mexico. day of the dead. They dress up in costumes to amuse the spirts of passed loved ones or something along those lines. Trick or treating on the other hand, I don't know where that came from. I think Americans made it
http://en.wikipedia.org/wiki/HalloweenIt's Celtic.
http://en.wikipedia.org/wiki/Day_of_the_DeadTechnically, it's diferent because it's a day later.
Also, with Trick-or-Treating, I think I can recall reading somewhere that it started out as an English thing.
Apparantly legend has it that pixies/fairies would come out into the world, and dress themselves up as beggars and poor people. They'd then say to people "Trick or Treat" and if the person gave them something nice (A Treat) they'd be blessed with good luck, however if the person didn't give them anything they'd put a curse on them (A Trick)
That's probably not the exact way it came around, but it's how I remember it's origin.
Also, it could be either English or American. I know that from what I read, people started doing "Trick or treat" at the same time that America was under English rule.