I really have a hard time understanding the context in which this was necessary. It seems to me like Sherman's March occurred at a time where the south was already on the brink of defeat. Why, then, would he need to destroy the infrastructure of Georgia on his march from Atlanta to Savannah?
Edit: I would just like to add that I live in Georgia, so my sources and understanding of the subject are probably biased. I just would like to hear some more objective perspectives. I know he wrote his Memoirs... but it is just to long to bother reading. If anyone has read it, what specific sections can I refer to to clear things up? It doesn't seem like the political landscape is well laid out in his memoirs either.
Sherman's March to Savannah (popularly coined his march to the sea) was entirely necessary, and played a crucial role in expediting the end of the Civil War. You spoke of context as it concerned the timing of the march within the scope of the war at that time (Sept. 1864), so let's start there. Although the war seems to have been wrapping up at that time to modern observers, the issue was still very much in doubt during September 1864, when Atlanta fell. The previous months had seen Sherman largely stymied by Gen. Johnson's efforts to keep his northern adversary from routing or driving off the Rebel forces in "the West." This, combined with Grant's inability to bag Lee (Grant's forces were stalled outside of Petersburg at this time) meant that the northern war effort had ground to something of a halt (thus, to answer your question, the South was decidedly NOT on the brink of defeat at this time). This was all in the midst of a Presidential campaign that threatened to drive Lincoln from office and replace him with McClellan, a man who was open to the idea of restoring the Union via peace negotiations with the South. This was a very dangerous time for the Union, and represented maybe the biggest challenge to the country in terms of a realistic threat of permanent separation. Once Sherman routed Gen. Hood (Johnson's replacement) he had an opportunity to take Savannah (a key Rebel port) and smash the Confederates' wartime industrial machine while en route. The combined effect of smashing a Confederate army, seizing a key Confederate stronghold, and wrecking the South's ability to make war had an ENORMOUS impact on the election, but also the rank and file of the Confederate army (east and west). Hundreds if not thousands of Rebel soldiers deserted to look after the farms and cities that Sherman was destroying, the Confederates' ability to make and prosecute the war was irrevocably dashed, and the Northern peace movement was dissolved. These were three HUGE factors that led to the end of the war, and had an unmistakable impact on Lee and Davis' ability to continue the rebellion. Sherman's march to the sea, which started during the middle of November, was thus a very important component of the Northern war effort that represented a political victory, but also robbed the South of the practical means to prosecute the war (by robbing them of rail lines, factories, and manpower). It should also be noted that Sherman didn't stop when he hit Savannah: he went to South Carolina next (which got it even worse than Georgia). So there was about 6 months between the start of Sherman's march to the sea and the actual end of the war, which hardly portends to the last gasp of the conflict. Had Sherman not taken such decisive action during this period, the war might have gone on much, MUCH longer, or worse, might have led to a McClellan election: something that might have doomed the Union altogether. [Sources: Bruce Catton, 'A Stillness at Appomattox'; Shelby Foote, 'The Civil War, A Narrative, v. 3'; James McPherson, 'Battle Cry of Freedom']
It seems to me like Sherman's March occurred at a time where the south was already on the brink of defeat.
The march started November 15, 1864. But Lee surrendered to Grant on April 9, 1865, and Johnston didn't surrender to Sherman until April 18, 1865. Hence it was about 5 months between the start of the march and Johnston surrendering to Sherman. Obviously at the start of the march things didn't look good for the South, but the war continued for some time after.