It's about modern day Americans celebrating the Native Americans and the Settlers getting together and eating in a mutually patronizing way this one time.
No, really. Basically, the settlers were starving to death after having spent the entire time not growing crap and not being good at knowing what was edible.
So, they went to the Native Americans and were all like "we're hungry here." To the Native Americans, this culturally meant "We're stupid, and don't even know that winter was cold, and that turkeys are edible! Please treat us like retarded children!" Accepting something for your survival and not the other side not expecting anything in return was more than a little bit of an insult.
And the Settlers took it as "You are superior and so's your God! Have this tribute to your superiority! Now please take away our land and treat us like shit!"
And we did. So we eat Turkeys to celebrate.
Oh, and there's some idea that it was all very familial, across even national and language barriers, etc, etc. But really, it started as one giant pissing match both sides were convinced had won. Which is actually a summation of all my Thanksgivings growing up right there.
Sorry for assuming you care if you don't!