Why were so few civil war battles fought on northern soil?

So let's make this simple, while most of the major battles of the Civil War were fought in Confederate territory, the battles of Antietam and Gettysburg took place inside the Union. Both were the result of Confederate General Robert E. Lee's attempt to reduce the pressure on the Confederate capital by striking north. Neither battle proved successful for the Confederacy, and both were typified by extremely high casualty counts.

D. a conflict between her competing identities.