According to Diana Karter Appelbaum's Thanksgiving: An American Holiday, an American History, the date of the "first" Thanksgiving is debatable. 1621? 1623? 1630? All have been claimed to've been the first.
While the holiday has been celebrated since [see above], it was first declared a national holiday by George Washington in 1789. Before this, various days were declared "Thanksgiving" in order to either fast, pray, feast, or celebrate military victory. (Note: I sure am glad that whole "fasting" thing died out.) However, it must be noted that the south saw Thanksgiving as a Yankee holiday; eventually it changed its mind. (Note: thank goodness.)
In 1863, Abraham Lincoln declared the last Thursday in November to be Thanksgiving, but "a Thanksfiving proclaimed not in celebration of military victory but in gratitude for a 'year filled with the blessings of fruitful fields and healthful skies'" (153). After this, Thanksgiving was celebrated by proclamation each year, but didn't become an official federal holiday until 1941.
Think the holidays have become too commercial? You can blame Franklin Roosevelt if you want. He's the one who had the big idea to move the holiday to the third Thursday in November instead of the last Thursday in November in order to allow for an extra week of Christmas shopping. This led to some folks calling the new date "Franksgiving" or "Democratic Thanksgiving" and the old date "Republican Thanksgiving."
During World War II, the Army promised that no soldier would eat canned turkey on Thanksgiving. . .and apparently they made good on their promise (although prisoners of war in Japan and Germany were sent canned turkeys via the Red Cross). Check out this guy enjoying his turkey leg:
So there you have it! Thanksgiving nuggets! (And in case you're wondering, there are plenty of Emily Dickinson poems that address Thanksgiving-esque themes.)
Have a safe and happy Thanksgiving, everyone.
Appelbaum, Diane Karter. Thanksgiving: An American Holiday, an American History. Facts on File, 1984.