The reality of the original Thanksgiving is that there was never a single event that directly contributed to the creation of the holiday. In actuality, a large portion of the food consumed on these special occasions by the colonists and Wampanoag Indians was the result of their laborious fall harvest, which was largely composed of grain. Thanksgiving as we know it today is the result of numerous harvests that led to gatherings and feasts. When other crops failed, this NMAI article claims that Indian corn was the only thing that kept everyone alive.
President Lincoln didn't even use the term Thanksgiving until 1863, not 1621, as Time Magazine claims. Franklin Roosevelt did not declare it a national holiday until he became president after that.
Thanks,
Eddie