Invasion through the Gap:
For the North, Cumberland Gap was a natural invasion route into the South -- providing access to vulnerable railroads and valuable minerals and salt works in East Tennessee and southwest Virginia.
For the South, the Gap was a gateway for an invasion of Kentucky to drive out the Federal foe.
Cumberland Gap exchanged hands four times during the Civil War:
August, 1861: Confederates fortify Cumberland Gap.
June 18, 1862: Union forces under General Morgan occupy the Gap.
September 17, 1862: Confederate General Stevenson forces evacuation of Union troops from the gap as the Confederates push into northern Kentucky's Bluegrass region begins.
September 9, 1863: Union forces under General Burnside accept surrender of General Frazier's 2,300-man Confederate garrison at the Gap.
Cumberland Gap remains in Northern hands for duration of the war.