[tanknetter]

The truth is that Confederate troops typically did as much damage as they could whenever they invaded Union states.

Indeed, that was usually a main purpose of their raids -- to secure supplies for themselves and destroy the Union's facilities.

Sure, the example of Lee in Pennsylvania is often cited, but it was more the exception than the rule for Confederate forces operating in Union states & territories.

True Union states and territories, or border states and territories?

I'd consider the two vastly different. Missouri, Kansas and Kentucky for instance saw an enormous amount of brutality - by both sides - that had more to do with the fact that the side those states was going to take was indeterminate. At least in the eyes of a lot of the local population. Plus there were very long-standing internal animosities and feuds in those states that the Civil War allowed to spill into the open.

[BroJoeK]

tanknetter: "True Union states and territories, or border states and territories?"

First of all, all Union states and territories were "true", regardless of what some Confederates may have wished.
None ever voted to secede, and all supplied more troops to the Union than Confederacy.

Second, all Border States had significant slave-holding populations, but they were distinct minorities, and were unable to control either politically or militarily.
They could however challenge the majority Unionists, and did so, often with very destructive results.

In some cases these were comparable to "scorched earth" policies practiced by some Union forces at war's end.