Many years ago, the first European settlers in New England celebrated a religious holiday.
They had set out to begin a new life on the far side of the Atlantic Ocean from their homeland. They had suffered terribly in the voyage, and during the first hard winter in Plymouth, Massachusetts. That first year, they had attempted to run their farm communally, and had a very poor harvest.
The following year, the leaders of the community let each family farm their own land, and give each family the profit from their land.
(The colony had depended on investors for startup money. The charter gave the investors the profits from excess grain sent back across the Atlantic. The original communal farm had been an attempt to collectively grow grain for that purpose. Except that they'd barely grown enough for starvation rations for themselves, that first year.)
This second year, the colony found a plentiful harvest.
They had also had, during those two years, good relations with the local Natives. So when the men of Plymouth had their celebration, they inviting the local Native to join.
The feast had wild turkey, venison, sea-food, beans, cranberries, pumpkin, as well as corn and grain. It also featured much conviviality.
The day was also a religious celebration: the men gave thanks to God, and rejoiced in the abundance of their harvest and in Divine generosity.
This mixture--the fruit of harvest, a ritual of thanks to God, and a gathering with family and friends--is the American holiday known as Thanksgiving.