You're all familiar with the traditional depiction of "The First Thanksgiving" in 1621 (or was it 1623?) at the Plymouth colony in what was to become the state of Massachusetts. You know, Pilgrims, Massasoit, Squanto, etc. feasting on venison, fish, corn, and of course, turkey.
But wait! This may all be a dastardly English (or "New English") plot to cover up the true history of Thanksgiving in North America, and to conceal the (alleged) fact that this holiday actually had its origins in -- FLORIDA!
There is evidence (read about it here) that the Thanksgiving feast tradition actually began in June, 1564, when a contingent of French Calvinists, or Huguenots, landed near the mouth of the St. Johns River near present-day Jacksonville, and promptly held a service of “thanksgiving” at the site of what would become Fort Caroline. Then there are those who insist that the First Thanksgiving was celebrated on September 8, 1565, when 600 Spanish settlers, under the leadership of Pedro Menéndez de Avilés, landed at what is now St. Augustine and immediately held a Mass of Thanksgiving for their safe delivery to the New World, followed by a feast of thanksgiving with the Timucua Indians, at which all dined on bean soup. Perhaps vexed that his own First Thanksgiving celebration had been upstaged by those snooty Frogs, Menéndez skipped dessert (more bean soup?) and promptly led his soldiers up the coast to Fort Caroline, where they massacred the Huguenots (read all about it here).
Wherever it all started, we know that Thanksgiving first became a nationally-recognized, annual holiday in the wake of President Abraham Lincoln's proclamation of a Thanksgiving Day to be celebrated by all Americans on the final Thursday in November 1863 (read the proclamation here) This prompted a massive, Union-wide outpouring by private citizens of generosity to soldiers then in the field or garrison, in the form of turkey, pies, bread, and other foodstuffs, which were collected by various committees and distributed in the camps by the Army itself. It should be noted that Jefferson Davis also declared a Confederate Thanksgiving day for November 16, 1864, but by then Atlanta was in ruins, Sherman was devastating Georgia, and there was little cause for celeberation--or means with which to celebrate--anywhere in the South (read about Thanksgiving in the Civil War here).
You've probably worked up a big appetite trying to digest all this astonishing information, so go eat a big turkey dinner with your family and friends! But before you do, remember to remember our fore-fathers and mothers, who endured so much to found, build, and defend this country so that we might enjoy all these blessings year after year. Most especially, remember all those who are now serving our country far from home, and do what you can, all year, to brighten their days.