Was it religious? Not purely. Was it both Indian and English? Very much so. Did it last several days? Yes. Was it friendly and peaceful? As much as any event with guys and games can be.
The annual “Let’s Beat Up on Thanksgiving” festivals out of academia and elsewhere have been overshadowed by other things, but they didn’t go away completely. As usual, Straw Puritans get dragged out of the dusty depths of history, dour, black-clad, and scowling. They are inflexible patriarchs who follow a hard, intolerant religion and who took advantage of the relative weakness of the Native peoples around the area, then betrayed the Natives and destroyed them.
As that great song says, “It ain’t necessarily so.” First off, Puritans could be dour, but usually were not. They didn’t wear black because it was too expensive for most of them (most. The man in the Court of James I with the canary yellow silk suit must have been impressive.) They did scowl, and laugh, and smile, and cry, and rejoice. Their faith was hard, but so were pretty much all faiths in Europe and England at the time, because of what was going on in the name of G-d and monarchs who thought at G-d was on their side. When you lose half your children before age 5, move across the sea twice to worship in peace, then deal with a New England winter, your meeting house/hospital burning, and so on, you cling tightly to faith.
The Plymouth Puritans were not inflexible, unlike some of the Massachusetts Separatists and later groups. The Plymouth congregation believed that revelation was on-going, and that interpretations changed and grew as people’s understanding and faith grew. Now, one had to be careful not to trust personal ideas and opinions too much, but the Plymouth believers remained open to change.
Their treaty with the Wampanoag Massasoit (a title, not a name) lasted for several years, until outside pressures proved too much. What the Plymouth settlers took from Indian caches, they tried to replace and pay back as they could. They shared, as did the Indians, and had treaties of mutual protection. Yes, there were misunderstandings. Yes, problems developed because of irreconcilable differences about what ownership of land meant, and what was empty land vs. resting land. But in the beginning things went tolerably well. Both groups needed each other, and knew that.
So the first New England Thanksgiving started with the Pilgrims in 1621. The Indians heard a hunting party, inquired what was up, and brought more food to the party. The Wampanoag people too had feasts of thanks to their deities, and both sides understood the solemnity and need to acknowledge the generosity of the Great Spirit(s). Both sides had enemies, physical and spiritual. The Pilgrims knew of the terrible war raging in Europe. The Wampanoag knew of their enemies moving farther inland. For a few days, however, there was peace, and good will, and feasting.
Francis J. Bremer. One Small Candle: The Plymouth Puritans and the Beginning of new England (Oxford, England: Oxford University Press, 2020)