Prior to 1863 states had their own Thanksgiving on different dates. Lincoln made it a national holiday on the last Thursday of November.
Then FDR changed it to the third Thursday in November to lengthen the Christmas shopping season for the merchants.
Families were split, observing Thanksgiving on different days depending whom they voted for.
Nowadays the T-day battleground is Debbie Downer vs `crazy rightwing uncle’, or else it’s Mom & Dad vs their new SJW college monsters.
Were the different dates centered around the local harvest times?