Comment by skissane

Thanksgiving, as a consistent national holiday formally observed every year, was established by Abraham Lincoln’s proclamation in 1863, which declared it a day for “Thanksgiving and Praise to our beneficent Father who dwelleth in the Heavens”. Clearly religious in nature, although no doubt Lincoln had political motivations as well - the two are not mutually exclusive. 1621 was in itself a one-off event; the fact that it was later cited as justification for a regular observance says more about those later times than about 1621, and how 1621 was presented at those later times (such as in 1863, but also various earlier times too-it was observed at the state/local level, and intermittently nationally too, before Lincoln made it a regular national observance) is more important than what really happened for the purpose of determining whether it should be classified as religious. Abraham Lincoln appears to have not believed in Christianity personally (his personal beliefs are obscure, but he may have been some kind of deist); but when he made that proclamation I think he was expecting most Americans to understand it in Christian terms and most Americans at the time in fact did.