Plimoth Patuxet Museum. Americans have long thought the history of the American holiday Thanksgiving to be relatively simple. The actual story of how the story of “the First Thanksgiving” was written and retold and how the holiday was developed and embraced by a nation is surprisingly complex. In many respects, the growth of the distinctly American holiday and the myth associated with it parallels (and continues to parallel) the development of the nation itself. In this unit, students will explore how the 1621 harvest feast came to be known as the First Thanksgiving, the country’s protean holiday, and how the meaning of the holiday changes as new meaning is layered.