That's a questionable claim.
No, its not a questionable claim, its a nutty claim. The war was won ten days earlier at Gettysburg and Vicksburg; although it would drag on for twenty months, Lee had lost the ability to maneuver and the South had lost Texas, Louisiana and Arkansas with the fall of Vicksburg and the capture of the Miss. River. Once they arrived in Manhattan, it took the Union Army, including many disabled soldiers (the Invalided ones) about 15 minutes to take on and clear out the mob of rioters in New York, “tough guys” in a mob (some of whom had burned down a black orphanage with the kids in it) but who went running, terrified, for shelter at the first sign of the Army.