How important was it to control “interior lines” during the Civil War?


Commanding view from Fort Donelson overlooking the Cumberland River

His first task as a department head was the daunting responsibility of maintaining a long and meandering defensive line which ran from the hills of eastern Kentucky to the Mississippi River . . . . He was all too aware that if the far right flank caved in there would be serious problems in Tennessee, and Kentucky would surely be lost.

Jacobson, Eric A. (2013-11-01). For Cause and Country: A Study of the Affair at Spring Hill & the Battle of Franklin (Kindle Locations 289-290). O’More Publishing. Kindle Edition.

Sherman’s two great campaigns through the interior of the South, first through Georgia and then through the Carolinas, were enormously important in weakening both the ability and the will of the southern people to carry on a hopeless fight. The very fact that Sherman was able to march his troops hundreds of miles through the interior of what purported to be the Confederacy, seemingly unhindered by any efforts of the Confederate army, was evidence of the helplessness of the slaveholders’ republic. The marches did enormous damage to the Confederacy’s continued ability to support armies in the field, destroying warehouses, depots, stockpiles, factories, and hundreds of miles of railroad track.

Woodworth, Steven E. (2011-04-16). This Great Struggle: America’s Civil War (Kindle Locations 5933-5938). Rowman & Littlefield. Kindle Edition.

Linked to the problem of supply was the concept of lines of operations. No matter how different in size two armies might be, the only thing that mattered was the size of the force each army could bring to a battlefield at a given moment (i.e., even an army that is numerically inferior to its opponent can still achieve victory if it can manage to pick off small sections of the enemy army and defeat them piece by piece). Consequently, Mahan impressed on his West Point pupils the vital importance of operating defensively on “interior lines” and forcing the enemy to operate on “exterior lines.” (What this means is that in any given strategic situation, an army occupying the interior of a position only has to move the chord of the arc surrounding that position to get from one end of it to the other; a commander on the exterior of a position has to occupy as well as move around the circumference of the arc, which forces him to spread his troops more thinly to cover the greater distance, and take more time in moving from point to point along the arc.) By taking up “interior lines,” a numerically inferior army could defend itself more easily, and could move to strike at exposed positions along the enemy’s arc faster than the enemy could reinforce them. For an attacking army, the best way to overcome the advantage of interior lines was to outflank the enemy’s lines entirely by means of turning or flanking movements. Hence, Civil War battles often found themselves determined by how successful one army was at getting hold of the other’s flank and compelling a withdrawal, rather than by head-to-head attacks.

Guelzo, Allen C. (2012-04-20). Fateful Lightning: A New History of the Civil War and Reconstruction (pp. 149-150). Oxford University Press. Kindle Edition.

The Confederates eventually synthesized these various strands of strategic theory and political reality into what Davis called an “offensive-defensive” strategy. This consisted of defending the Confederate homeland by using interior lines of communication (a Jominian but also common-sense concept) to concentrate dispersed forces against an invading army and, if opportunity offered, to go over to the offensive, even to the extent of invading the North. No one ever defined this strategy in a systematic, comprehensive fashion. Rather, it emerged from a series of major campaigns in the Virginia-Maryland and Tennessee-Kentucky theaters during 1862, and culminated at Gettysburg in 1863.

McPherson, James M. (2013-01-28). Battle Cry of Freedom: The Civil War Era (Kindle Locations 7206-7211). ACLS Humanities E-Book. Kindle Edition.

Given the advantages of fighting on the defensive in its own territory with interior lines in which stalemate would be victory against a foe who must invade, conquer, occupy, and destroy the capacity to resist, the odds faced by the South were not formidable.

McPherson, James M. (2013-01-28). Battle Cry of Freedom: The Civil War Era (Kindle Locations 17673-17675). ACLS Humanities E-Book. Kindle Edition.

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