In March 1621, representatives of the Wampanoag Confederacy_—the Indigenous people of the region that is now southeastern Massachusetts—_negotiated a treaty with a group of English settlers who had arrived on the Mayflower several months earlier and were struggling to build a life for themselves in Plymouth Colony.

The peace accord, which would be honored on both sides for the next half-century, was the first official treaty between English settlers and Native Americans, and a rare example of cooperation between the two groups. On the orders of their leader, Ousamequin (known to the settlers as Massasoit), the Wampanoags taught the English men and women how to plant crops, where to fish and hunt, and other skills that would prove critical to the new colony’s survival. To celebrate the first harvest at Plymouth, Governor William Bradford and the other settlers invited the Wampanoags for a celebratory feast in November 1621, now remembered as the first Thanksgiving.

As the Wampanoags left few written records, most of what we know of the treaty and its aftermath comes from English chroniclers of Plymouth Colony’s history, namely Bradford and his fellow Pilgrim Edward Winslow. But in focusing on the Plymouth colonists, familiar versions of the story often gloss over the Wampanoags, their motivations for seeking a peace treaty with the English settlers in 1621 and the benefits they_—at least temporarily—_gained from the alliance.

From the moment the Mayflower arrived off the coast of Massachusetts in November 1620, the Wampanoags in the region had watched the new arrivals closely, but kept their distance. Previous European explorers, beginning with Giovanni da Verrazzano in 1524, had initially been welcomed for the trade possibilities. That changed after 1614, when Captain Thomas Hunt kidnapped a group of Wampanoags from the community of Patuxet (the future site of Plymouth Colony) to sell into slavery.

Around 1616, an unknown disease likely brought by European traders struck the Wampanoags and other Native American tribes in the region. Candidates for the mysterious disease have ranged from smallpox or measles (or a combination) to yellow fever to cerebrospinal meningitis, while a 2010 study suggested a bacterial infection known as leptospirosis.

While contemporary accounts from English sources referred to “the plague,” bubonic plague has been widely discounted, according to historian David J. Silverman. He argues that the most likely culprit was malignant confluent smallpox, which would have caused the combination of symptoms—headache, spots, sores (pox), yellowing of the skin—that victims reportedly showed.

Whatever the plague was, it decimated the Indigenous groups in the region where Plymouth Colony would soon be founded. By one account, the Wampanoag nation lost an estimated two-thirds of its population, or as many as 45,000 people.

By 1620, Wampanoag weakness had provided an opportunity for a rival group to the west, the Narragansett, who had largely escaped the impact of the disease. When the Plymouth settlers arrived, Ousamequin was struggling to prevent the Narragansett from subjugating the remaining Wampanoags and forcing them to pay tribute. While he initially kept his distance from the Mayflower’s inhabitants, fearing further aggression—and disease—Ousamequin evidently came to the conclusion that an alliance with the new English arrivals in the region could help protect his people.

After sending Samoset, an Abenaki chief (possibly a captive of the Wampanoag) who knew some English, as an emissary to the Plymouth settlers on March 16, 1621, Ousamequin arrived about a week later. He and Governor John Carver negotiated the treaty with the help of Tisquantum (Squanto), a Wampanoag from Patuxet who had been among the group captured by Hunt in 1614. Tisquantum had managed to escape slavery and lived briefly in England before returning home in 1619 aboard another English ship.

As Bradford and Winslow later wrote in Mourt’s Relation (1622), “[Ousamequin] has a potent adversary in the Narragansetts, that are at war with him, against whom he thinks we may be of some strength to him, for our pieces [guns] are terrible to them.” In the treaty, the Wampanoags and the Plymouth settlers, on behalf of King James I, agreed to keep peace between them, as well as to defend each other against potential attacks by other Indigenous groups.

For the Pilgrims and other settlers at Plymouth Colony, the peace treaty with the Wampanoag meant learning the skills they needed to attain that first successful harvest—and to survive. For Ousamequin, the treaty meant preserving his people’s autonomy and his own power and influence, as even some Wampanoags bitterly disagreed with his decision to align with the English colonizers.

Carver died in April 1621, but Bradford and Winslow, his successors, continued to honor the treaty with the Wampanoags. Despite periodic tensions, peace between the two groups survived until after Ousamequin’s death in 1661, making the 1621 treaty the only one between Native Americans and English colonists to be honored throughout the lives of all who signed it.

The peace, however, would not last. Ousamequin’s first son and successor, Wamsutta, died in 1662 amid negotiations with the colonists over land. He was succeeded by his brother Metacom, later known as King Philip, who claimed Wamsutta had been poisoned. Escalating tensions between Plymouth Colony and a coalition of tribes under Metacom’s command would explode into King Philip’s War (1675-78), a bloody conflict that led to Metacom’s execution in 1676 and the killing or capture of thousands of Native Americans.