The commonly accepted history of Thanksgiving is based almost entirely on myths. And this is the easiest place to start researching the history of Thanksgiving.
The reason that we have so many myths associated with Thanksgiving is that it is an invented tradition. It doesn't originate in any one event. It is based on the New England puritan Thanksgiving, which is a religious Thanksgiving, and the traditional harvest celebrations of England and New England and maybe other ideas like commemorating the pilgrims.
James W. Baker, Senior Historian at Plimoth Plantation