How the Civil War Created Thanksgiving - NYTimes.com:
"...That fall, Lincoln had precious little to be thankful for.
The Union victory at Gettysburg the previous July had come at a dreadful cost – a combined 51,000 estimated casualties, with nearly 8,000 dead.
Enraged by draft laws and emancipation, rioters in Northern cities like New York went on bloody rampages.
And the president and his wife, Mary, were still mourning the loss of their 11-year-old son, Willie, who had died the year before.
So it might seem odd that Lincoln chose this moment to announce a national day of thanksgiving, to be marked on the last Thursday in November.
His Oct. 3, 1863, proclamation read: “In the midst of a civil war of unequaled magnitude and severity … peace has been preserved with all nations, order has been maintained, the laws have been respected and obeyed, and harmony has prevailed everywhere, except in the theater of military conflict.”
But it took another year for the day to really catch hold.
In 1864 Lincoln issued a second proclamation, which read, “I do further recommend to my fellow-citizens aforesaid that on that occasion they do reverently humble themselves in the dust.”
Around the same time, the heads of Union League clubs – Theodore Roosevelt’s father among them – led an effort to provide a proper Thanksgiving meal, including turkey and mince pies, for Union troops.
As the Civil War raged on, four steamers sailed out of New York laden with 400,000 pounds of ham, canned peaches, apples and cakes – and turkeys with all the trimmings.
They arrived at Ulysses S. Grant’s headquarters in City Point, Va., then one of the busiest ports in the world, to deliver dinner to the Union’s “gallant soldiers and sailors.”
This Thanksgiving delivery was an unprecedented effort – a huge fund-raising and food-collection drive.
One soldier said, “It isn’t the turkey, but the idea we care for.”"