It has nothing to do with the north or south.
The google site doesn't say that when you put 1st Thanksgiving in the subject line. If you put Berkeley Plantation they mention it. The internet is not always correct.
https://en.wikipedia.org/wiki/Thanks...(United_States)
The History of the First Thanksgiving History of Massachusetts Blog
Berkeley Plantation | FIRST THANKSGIVING
The First Thanksgiving Took Place in Virginia, not Massachusetts | Washingtonian