The war was not very close from a tactical standpoint. The North was much better supplied, manned, and technologically advanced. This is usually a big debate among historians. I fall under the category that the war was VERY close to being won by the South, but they lost the plot and got cocky. Their path to victory was through political victory, and political victory only. The South had to make the northern population convinced that the war was way too expensive, brutal, and costly to be fighting, and this was probably on path to being achieved. The issue arose when the South invaded the North. This caused two things to happen that led the South to eventually lose. The South was defeated badly in Gettysburg, and their army never recovered. It also caused the North to actually get more motivated to fight. When Lee went North his goal was to surround D.C., and then threaten it/siege it (probably could not have captured it, but who really knows). He thought by doing this he would crush Northern moral, instead, he scared/motivated northerners. The South was no longer defending their home, they were invaders, and they needed to be crushed. Not to mention, the North had proven they could achieve huge victories over the South.

If the South held out with their defensive tactics after their huge victories in northern Virginia (which they chose to capitalize on by invading the North), they would have eventually swayed the northern population that the war was too much, and if they could have held out to 1984 (the next election), Lincoln would have lost and the North would have backed off, assuming Lincoln did not back off himself already.