Thanksgiving is a justly popular holiday because it involves family, friends, food, and no need to shop for presents. <G> As you probably know, the holiday is a form of harvest festival so the origins are lost in the mists of time. The difference between a good harvest or a bad one was literally life or death, so it made great sense to celebrate the bounty of the earth.
I love Thanksgiving because it's secular and can be–and is!–celebrated by everyone, of all religious and ethnicities. It's a time for families, but also for inviting friends, particularly those who might not have someone else to celebrate with. Roast turkey is not mandatory.