Vicksburg National Military Park, Mississippi
"Vicksburg is the nail head that holds the South's two halves together...Vicksburg is the key." The Vicksburg NPS site is here.
Not the site of a major battle, but rather a 47-day siege. Vicksburg's surrender to Grant on July 4, 1863 (one day after the Union army's victory at Gettysburg) opened the Mississippi River to the US fleet and started the downfall of the Confederacy.
Taken October 18, 2014.
Vicksburg National Military ParkMississippiVicksburgcemeterysiegeNPSRichard Shattuck, from