Why did most of the worst fighting of the war take place in the south?

Answer 1

Because of the defensive strategy adopted by the Confederacy, which compelled the the Federals to invade the South, defeat its Armies and conquer its territory, in order to win the war and restore the Union.

Answer 2

Because it was principally a war of invasion by the Union armies, to destroy the Confederate armies, and latterly the civlian infrastructure that supported those armies.

The Confederates' overall strategy was to resist this invasion and try to destroy the Union armies. There was no immediate incentive to invade non-slave states.

It was not till the autumn of '62 that Lee saw the point of invading Pennsylvania, to impress the British, who were planning to aid the Confederacy. (This failed, and the British stayed out.)

The following summer, he tried again, this time for rather different reasons. The Confederacy was running out of all manner of vital supplies, and a raid of the prosperous state of Pennsylvania would enable replenishment - especially the boots and shoes the army so sorely needed, and Lee noted a big shoe facrory near Gettysburg.

Answer 3

The South was the part of the US that seceded. In order to win the Civil War, it only had to stay put and defend "its" territory. However, the North had to get the South back into the Union, so it had to conquer seceded territory in the South.

One of the very few battles fought in the North was Gettysburg - Robert E. Lee, the commander of the Southern troops wanted a decisive victory, almost like the one at Saratoga in 1777, in order to get help from outside nations. Striking at, and beating, the enemy in its own homeland would have raised Northern war weariness and might have gotten an ally for the South.