because only pilgrims to america were thankful for taking over native land and giving the locals disease and death in return

Thanks for the history lesson. Practically speaking, anyone could participate in Thanksgiving. It's a pretty simple holiday.
EDIT: Whoops, mega misread your post. Disregard all that...
It's this thing where, like, there's snow one minute, then WHAM. Foliage, foliage everywhere!