It was Sarah Josepha Hale, a 74-year-old magazine editor, who wrote a letter to  President Lincoln on 28 September 1863, urging him to have the "day of our annual Thanksgiving made a National and fixed Union Festival." She explained, "You may have observed that, for some years past, there has been an increasing interest felt in our land to have the Thanksgiving held on the same day, in all the States; it now needs National recognition and authoritive fixation, only, to become permanently an American custom and institution."

And Sarah got her wish with Lincoln issuing a proclamation on 3 October 1863, which included... 

"I do therefore invite my fellow citizens in every part of the United States, and also those who are at sea and those who are sojourning in foreign lands, to set apart and observe the last Thursday of November next, as a day of Thanksgiving and Praise to our beneficent Father who dwelleth in the Heavens. And I recommend to them that while offering up the ascriptions justly due to Him for such singular deliverances and blessings, they do also, with humble penitence for our national perverseness and disobedience, commend to His tender care all those who have become widows, orphans, mourners or sufferers in the lamentable civil strife in which we are unavoidably engaged, and fervently implore the interposition of the Almighty Hand to heal the wounds of the nation and to restore it as soon as may be consistent with the Divine purposes to the full enjoyment of peace, harmony, tranquillity and Union.":

Moving forward, some 180 years and Marianne wonderfully shares how that celebration has become an essential part of American culture…

"Thanksgiving strips away the commercial obligations that come with other holidays—no gifts to buy, no decorations to hang—and focuses on something beautifully simple: gather the people you care about, cook together, eat together, be together.

It doesn’t matter if you’re celebrating on the actual Thursday or the following Saturday. It doesn’t matter if your turkey came from an American supermarket or a British butcher who special-ordered it with a bemused smile. It doesn’t matter if you’re serving traditional sides or sharing recipes with British friends trying their hand at sweet potato casserole.

What matters is the gathering. The gratitude. The reminder that even in a fragmented, rushed world, we can still create space to slow down and be together.

That’s the part of Thanksgiving that follows me across the Atlantic. That’s why I still celebrate it, still insist on making the effort, still feel that quiet homesickness on the fourth Thursday of November even while building new traditions in a new country.

Because the good holidays aren’t really about the place or the timing or even the specific foods. They’re about what we do when we gather, who we choose to gather with, and the gratitude we share for having people worth gathering for."