Hanna, you know I respect the heck out of you.
That said, Halloween is a Gaelic harvest festival (viz Wiki). It has its roots in Gaelic countries... not America. Back when this day was considered serious (instead of the tongue-in-cheek thing it is now), there had only been a handful of Gaelic-blooded people to have ever been to America! We picked it up against the grain as it was not wholeheartedly supported by any major religion. Yet it survived in our culture, strangely enough..
Is it so strange that England, attached to a Gaelic country on one end, and just over the water from another, should celebrate this Gaelic holiday?
Holidays that are native to America would have to come from the First Nations peoples, and for the most part, no one's ever heard of them beyond the tribes: Powamu, Midwinter Ceremony, Green Corn Dance,etc...
We like Halloween here, but only as a novelty, and like most everything else here's it's imported. =)