In 1789, President George Washington proclaimed the first national holiday of Thanksgiving. He chose a date in late November for people to express gratitude for “the great degree of tranquility, union, and plenty,” along with the “civil and religious liberty” that the burgeoning United States of America enjoyed.

(SOURCE) https://www.cnn.com/2022/11/27/opinions/three-things-george-washington-gave-thanks-opinion-column-galant/index.html