The
Pilgrims who sailed to this country aboard the Mayflower were originally
members of the English Separatist Church (a Puritan sect). They had earlier fled
their home in England and sailed to Holland (The Netherlands) to escape
religious persecution. There, they enjoyed more religious tolerance, but they
eventually became disenchanted with the Dutch way of life, thinking it ungodly.
Seeking a better life, the Separatists negotiated with a London stock company to
finance a pilgrimage to America. Most of those making the trip aboard the
Mayflower were non-Separatists, but were hired to protect the company's
interests. Only about one-third of the original colonists were Separatists.
The Pilgrims set ground at Plymouth Rock on December 11, 1620. Their first winter was devastating. At the beginning of the following fall, they had lost 46 of the original 102 who sailed on the Mayflower. But the harvest of 1621 was a bountiful one. And the remaining colonists decided to celebrate with a feast -- including 91 Indians who had helped the Pilgrims survive their first year. It is believed that the Pilgrims would not have made it through the year without the help of the natives. The feast was more of a traditional English harvest festival than a true "thanksgiving" observance. It lasted three days.
Governor William Bradford sent "four men fowling" after wild ducks
and geese. It is not certain that wild turkey was part of their feast. However,
it is certain that they had venison. The term "turkey" was used by the
Pilgrims to mean any sort of wild fowl. 
Another modern staple at almost every Thanksgiving table is pumpkin pie. But it is unlikely that the first feast included that treat. The supply of flour had been long diminished, so there was no bread or pastries of any kind. However, they did eat boiled pumpkin, and they produced a type of fried bread from their corn crop. There was also no milk, cider, potatoes, or butter. There was no domestic cattle for dairy products, and the newly-discovered potato was still considered by many Europeans to be poisonous. But the feast did include fish, berries, watercress, lobster, dried fruit, clams, venison, and plums.
This "thanksgiving" feast was not repeated the following year. But in 1623, during a severe drought, the pilgrims gathered in a prayer service, praying for rain. When a long, steady rain followed the very next day, Governor Bradford proclaimed another day of Thanksgiving, again inviting their Indian friends. It wasn't until June of 1676 that another Day of Thanksgiving was proclaimed.
On June 20, 1676, the governing council of Charlestown, Massachusetts, held a
meeting to determine how best to express thanks for the good fortune that had
seen their community securely established. By unanimous vote they instructed
Edward Rawson, the clerk, to proclaim June 29 as a day of thanksgiving.
October of 1777 marked the first time that
all 13 colonies joined in a thanksgiving celebration. It also commemorated the
patriotic victory over the British at Saratoga. But it was a one-time affair.
George Washington proclaimed a National Day of Thanksgiving in 1789, although some were opposed to it. There was discord among the colonies, many feeling the hardships of a few Pilgrims did not warrant a national holiday. And later, President Thomas Jefferson scoffed at the idea of having a day of thanksgiving.
It was Sarah Josepha Hale, a magazine editor, whose efforts eventually led to what we recognize as Thanksgiving. Hale wrote many editorials championing her cause in her Boston Ladies' Magazine, and later, in Godey's Lady's Book. Finally, after a 40-year campaign of writing editorials and letters to governors and presidents, Hale's obsession became a reality when, in 1863, President Lincoln proclaimed the last Thursday in November as a national day of Thanksgiving. He did this to unify the country in a time when civil war divided the country.
Thanksgiving was proclaimed by every
president after Lincoln. The date was changed a couple of times, most recently
by Franklin Roosevelt, who set it up one week to the next-to-last Thursday in
order to create a longer Christmas shopping season. Public uproar against this
decision caused the president to move Thanksgiving back to its original date two
years later. And in 1941, Thanksgiving was finally sanctioned by Congress as a
legal holiday, as the fourth Thursday in November.