What's the historical significance of Abraham Lincoln's Thanksgiving Proclamation?

Lincoln's Thanksgiving Proclamation, which declared the final day of November a national day of "thanksgiving and praise to Almighty God," was one of many similar declarations by American Presidents, usually in times of crisis. Lincoln's proclamation standardized the celebration of Thanksgiving. Before the Civil War, many states celebrated days of thanksgiving at different times of the year. After Lincoln's proclamation, all states, at least in the North, celebrated the holiday simultaneously. With World War II...

Lincoln's Thanksgiving Proclamation, which declared the final day of November a national day of "thanksgiving and praise to Almighty God," was one of many similar declarations by American Presidents, usually in times of crisis. Lincoln's proclamation standardized the celebration of Thanksgiving. Before the Civil War, many states celebrated days of thanksgiving at different times of the year. After Lincoln's proclamation, all states, at least in the North, celebrated the holiday simultaneously. With World War II looming, Franklin Roosevelt signed legislation moving Thanksgiving, now an official federal holiday, to its current date of the fourth Thursday in November. But Lincoln's proclamation was the first to make Thanksgiving a truly national holiday. His proclamation also illustrates the extreme stress the nation experienced during the Civil War, and the ways in which statements of religious faith historically played a role in national public life. Like many other Lincoln speeches, this proclamation is also studied for its rhetorical power, evoking divine assistance in the midst of an extraordinary crisis.