Jennie A. Brownscombe's 1914 fantasy of "The First Thanksgiving at Plymouth" has many inaccuracies—it shows only a small gathering (there would have been more than 300 people at the actual event, about two-thirds of them Pokonokets*), and details such as the frontier-style log cabin sitting out in the open and the plains Indian warbonnets are wildly out of place. The costumes of the Pilgrims (who would have called themselves Separatists, if they needed a name for themselves at all) are all wrong. The painting is more about an idea than it is a representation of history—the idea of people setting aside cultural differences, offering each other mutual aid and succor, and feasting together and giving thanks to God.
Harvest celebrations predate A.D. 1621 by thousands of years, of course, and both the Indians and the Europeans would have already been well familiar with their respective traditions of harvest feasts held in the fall of the year.
If you celebrate the day, wherever in the world you are, a good day to you and yours. And, whether you give particular thanks this day or not, may you and your family have much for which to be grateful in the coming year.
(P.S. TOP will be closed for a couple of days, but I'll probably be back by Sunday. I'm assuming I won't be able to stay away.)
*The natives at the first Thanksgiving were members of the Pokonoket tribe, of the Wampanoag confederacy or nation. Wampanoag means "people of the east." The leader and chronicler of the pilgrims, my ancestor William Bradford, was confused as to whether "Massasoit" was a title or a name, a confusion which persists right down to the present. It was a title; the Massasoit's name was Ousamequin, sachem (chief or leader) of the Pokonoket and massasoit (great sachem) of the Wampanoag.
It's interesting that Pokonoket means "people of the clearing." The Wampanoag had been decimated by European diseases in the years before 1620, and the area around Plymouth was largely deserted when the Mayflower arrived—but the English had little clearing of the land to do, because the Pokonoket had already cleared fields for crops.
Although the pilgrims, Thanksgiving, and Plymouth Colony are mostly considered fit for study only by schoolchildren in the U.S.—it's the national mythos aspect we really care about, not the actual history—we've been treated to a fine account of the era for general readers recently, in Nathaniel Philbrick's entertaining and readable book Mayflower.