I'm not exactly sure what you're seeing online, but if it's referring to what I assume it's referring to, the answer is both yes and no.

Let's start with the "no" side of things. The modern Thanksgiving has its legendary origins in the thanksgiving of 1621. Colonists at Plymouth were celebrating a good harvest and a successful hunting season. Their Wampanoag allies, alerted by the colonists' celebratory gunfire, went to investigate and ultimately joined in the party, bringing five deer as gifts. That's the peaceful, bringing-people-together incident that is referenced in the tales of Thanksgiving.

Now, on to the "yes" side of things. In October 1637, the New England colonists instituted an official Thanksgiving day. One of the things they were thankful for that year was the "subduing of the Pequots" during the Mystic Massacre, one of the most infamous and bloody clashes between the colonists and their indigenous neighbors. Between 400 and 700 Pequots were killed in the massacre.

In this post I go into more details concerning the Mystic Massacre. It also touches on the 1621 Thanksgiving, with a link to another post that gives even more details on that one.