Thanksgiving didn't come into the world fully formed. We don't even know when the first Thanksgiving Day took place, only that it was sometime between Sept. 21 and Nov. 9, 1621.
The Pilgrims certainly had no idea of founding an annual holiday, either. The first Thanksgiving was strictly a one-shot event. Similar ad hoc days of thanksgiving were proclaimed from time to time in Massachusetts over the next 50 years--usually by the churches, rather than by the civil authorities--but it was Connecticut that made Thanksgiving an annual event, starting around 1647.
The custom of having an annual Thanksgiving Day spread throughout New England in the 17th Century, but as yet it did not include any idea of commemorating the First Thanksgiving. If anything was commemorated, it was a later Thanksgiving when the crops had failed and the Massachusetts Bay Colony came very close to starvation.
In 1631, everybody was down to a daily ration of just five grains of corn when a day of fasting and prayer was proclaimed for Feb. 22. Miraculously, on that day a ship returned from England with food supplies, the colony was saved and the fast day turned into a feast. There is a very old New England custom, now mostly forgotten, of serving every diner five grains of corn before the meal in memory of the hardship and the deliverance of that year.
The holiday actually met a certain amount of resistance as it spread. Since the "pagan" holiday of Christmas was not celebrated in Massachusetts until the 19th Century, Thanksgiving was often thought of as essentially a Puritan substitute for Christmas.
Thanksgiving made no headway in the South, for instance, and probably it was only because the Dutch colonists had celebrated what they called Thankday that it was accepted in New York. When the British governor of Rhode Island proclaimed Thanksgiving in 1687--doubtless thinking he was doing his subjects a big favor--Puritan-hating religious dissidents celebrated the holiday so contemptuously he threw some of them in jail. Rhode Island didn't start celebrating Thanksgiving until 1776.
In 1776, of course, Thanksgiving was not a Puritan but a Patriot holiday. That year and every year throughout the Revolutionary War, the Continental Congress declared a national Thanksgiving to boost morale. George Washington also declared Thanksgivings as President in 1789 and 1795, as did the following Presidents occasionally until about 1815.
Still, the holiday did not catch on. That took two things: the migration of New Englanders throughout the Northern states, enthusiastically taking their holiday with them, and one very determined lady, Sarah Josepha Hale.
Sarah Hale was born in Maine in 1788 and had powerful childhood memories of Thanksgiving. In 1826 she published a novel containing a plea for a national Thanksgiving holiday. In 1846, as editor of the influential Godey's Lady's Book, a combination fashion and literary magazine, she began her campaign in earnest. From then on, she wrote at least two editorials a year on the subject and deluged public figures with correspondence about the need for Thanksgiving. She even included a chapter on the campaign for a national Thanksgiving in her book on etiquette.
The South dragged its heels for a while--when the governor of Virginia considered the idea in 1855, it was denounced as a relic of Puritan bigotry (probably a code word for Northern abolitionism), but the next year his successor just proclaimed the holiday without soliciting advice, and it was a success.
In 1859, Thanksgiving was celebrated in every state of the Union except Delaware, Missouri and recently admitted Oregon, and Sarah Hale expressed the hope that the holiday could unify the country against the gathering clouds of the Civil War.
That didn't happen, of course, but during that war she persuaded Abraham Lincoln to declare a national Thanksgiving Day, intended to be celebrated annually. He established the date we follow now, the fourth Thursday in November. After the Civil War, Thanksgiving was encouraged as a way of healing the wounds of the struggle.
The menu at the first Thanksgiving in 1621 was simply whatever the Pilgrims, with the help of the friendly Wampanoag Indians, could put together: venison, wildfowl (mostly turkeys and ducks), fish and cornmeal. Even today, the Thanksgiving table is supposed to groan with abundance, but in the 19th Century it really groaned. Sarah Hale--whose vision obviously influenced how we celebrate Thanksgiving--described one table loaded with chicken pies, goose, ducklings and three kinds of red meat as well as turkey, and another crowded with plum puddings, custards and pies of all sorts.
She was emphatic, however, that turkey held pride of place among the meats and pumpkin among the pies, and these are still the essential Thanksgiving dishes for most people. How did they get this status?