“We Gather Together” is a Christian Hym of Dutch origin written in 1597 by "Adrianus Valerius". It was originally set to a Dutch folk tune and is now associated with "Thanksgiving" in the United States.
Thanksgiving was always celebrated in America but became a national holiday by a Presidential Proclamation of Abraham Lincoln on October 3rd 1863 in the midst of the Civil War.
The original date for Thanksgiving Day was set for Thursday November 26th.
Later in 1942 President Franklin D. Roosevelt through a joint resolution in Congress issued a proclaimed designating the 4th Thursday in November to be Thanksgiving Day regardless of the numerical date.
Thanksgiving began as a strictly religious holiday by now it is primarily an opportunity for families to get together.