'To many Native Americans, Thanksgiving is a "Day of Mourning" that marks the genocide of thousands of Native Americans, the theft of Native lands and the assult on Native cultures. A few hundred Native Americans plan to gather along Plymouth shore to tell the stories of their ancestors. ... Massachusetts Gov. John Winthrop might have declared 1637 the first official day of Thanksgiving, but for many of the nearly 3 million Native Americans, it's a cruel reminder of the massacre that year of 700 Pequot men, women and children by the Puritans, who had arrived a few years earlier on the Mayflower and were warmly greeted by Native Americans with food. Later, the visitors were given land, taught to plow, sow and tend to their crops.'
There are several gatherings of surviving native peoples around the country to hold "anti-Thanksgiving' events. One is held on Alcatraz Island, and this article discusses another held in Plymouth Rock Massachusetts.