Actually... "Halloween" have been celebrated since long before the US even existed. It has roots in the Celtic festival of Samhain and the Christian holy day of All Saints. And Trick-or-treating has been around since at least the 1600s England...
See more:
http://en.wikipedia.org/wiki/HalloweenAnd related articles =)
PS. The "Commercial" celebration with costumes, pumpkins and trick-or-treat didn't become popular in Sweden until the 1990s... Before that this was a strict religious tradition where EVERYTHING was closed! No movies, No Restaurants, No Stores open anywhere for two days...