Although the North wasn't the first to start using rails, they most certainly perfected this form of transportation after being overwhelmed by the Confederacy's use of it, which you can hear about here- http://www.voki.com/pickup.php?scid=9833320&height=267&width=200 . Rails were the backbone of Grant’s plan to target the South’s weaknesses. He used these to transport troops to Richmond and later on 20 miles South to Petersburg. The Union capture of Atlanta allowed for the disruption of the Confederation’s rail operations at their key junction city, ending any chance they had to get back into the railroad game. All of these led to Lee's surrender at Appomattox Courthouse.