The first Thanksgiving was not a “thanksgiving,” in Pilgrim terms, but a “rejoicing.” An actual giving of thanks required fasting and quiet contemplation; a rejoicing featured feasting, drinking, militia drills, target practice, and contests of strength and speed. It was a party, not a prayer, and was full of people shooting at things. The Indians were Wampanoags, led by Ousamequin (often called Massasoit, which was a leadership title rather than a name). An experienced diplomat, he was engaged in a challenging game of regional geopolitics, of which the Pilgrims were only a part.

…Nor did the Pilgrims extend a warm invitation to their Indian neighbors. Rather, the Wampanoags showed up unbidden. And it was not simply four or five of them at the table, as we often imagine. Ousamequin, the Massasoit, arrived with perhaps ninety men—more than the entire population of Plymouth. Wampanoag tradition suggests that the group was in fact an army, honoring a mutual-defense pact negotiated the previous spring. They came not to enjoy a multicultural feast but to aid the Pilgrims: hearing repeated gunfire, they assumed that the settlers were under attack. After a long moment of suspicion (the Pilgrims misread almost everything that Indians did as potential aggression), the two peoples recognized one another, in some uneasy way, and spent the next three days together.

…Why would Ousamequin decide to welcome the newcomers and, in 1621, make a mutual-defense pact with them? During the preceding years, an epidemic had struck Massachusetts Bay Indians, killing between seventy-five and ninety per cent of the Wampanoag and the Massachusett people. A rich landscape of fields and gardens, tended hunting forests, and fishing weirs was largely emptied of people. Belief systems crashed. Even survival did not mean good health, and, with fields unplanted and animals uncaught, starvation followed closely behind. The Pilgrims’ settlement took place in a graveyard.

Wampanoag people consolidated their survivors and their lands, and reëstablished internal self-governance. But, to the west, the Narragansetts—traditional rivals largely untouched by the epidemic—now outnumbered the Wampanoags, and that led to the strengthening of Ousamequin’s alliances with the surviving Massachusett and another nearby group, the Nipmucks. As the paramount sachem, he also had to contend with challenges to his leadership from a number of other Wampanoag sachems. And so, after much debate, he decided to tolerate the rather pathetic Pilgrims—who had seen half their number die in their first winter—and establish an alliance with them. 

…Ousamequin’s sons Pumetacom—called King Philip by the English—and Wamsutta began forming a resistance, despite the poor odds. By 1670, the immigrant population had ballooned to sixty or seventy thousand in southern New England—twice the number of Native people.

…Abenaki and other allies continued the struggle for years.

…New Englanders certainly celebrated Thanksgivings—often in both fall and spring—but they were of the fasting-and-prayer variety. Notable examples took place in 1637 and 1676, following bloody victories over Native people. To mark the second occasion, the Plymouth men mounted the head of Ousamequin’s son Pumetacom above their town on a pike, where it remained for two decades, while his dismembered and unburied body decomposed. The less brutal holiday that we celebrate today [did not take] shape [until] two centuries later. …In 1841, the Reverend Alexander Young explicitly linked three things: the 1621 “rejoicing,” the tradition of autumnal harvest festivals, and the name Thanksgiving.

…A couple of decades later, Sarah Josepha Hale, the editor of Godey’s Lady’s Book, proposed a day of unity and remembrance to counter the trauma of the Civil War. …Only later would it consolidate its narrative around a harmonious Pilgrim-Wampanoag feast. …American mythmakers discovered that the Pilgrims, and New England as a whole, were perfectly cast as national founders: white, Protestant, democratic, and blessed with an American character centered on family, work, individualism, freedom, and faith.

…The Thanksgiving story buries the major cause of King Philip’s War—the relentless seizure of Indian land. …Like most Colonial wars, this one was a giant slave expedition, marked by the seizure and sale of Indian people. …During the next two centuries, New England Indians also suffered indentured servitude, convict labor, and debt peonage, which often resulted in the enslavement of the debtor’s children.

…With so many men dead or enslaved, Native women married men outside their group—often African-Americans—and then redefined the families of mixed marriages as matrilineal in order to preserve collective claims to land. They adopted the forms of the Christian church, to some degree, in order to gain some breathing space. 

The Invention of Thanksgiving | The New Yorker

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