I think Sherman was engaged in attacking and attempting to destroy the means of production of th South in order to cripple it's capacity to make war and also to make the cost of war so heavy on the citizen's that they would accept peace.
I'm not sure if George Washington's attacks on native Americans falls into the rubric of terrorism, perhaps it was attempted genocide. I've read that Hitler studied Washington's campaigns and used them to develop his persecution of the Jews, but perhaps Washington would have claimed that like Sherman he was attempting to destroy the Indian's capacity for waging war.
Having written this I don't think it's possible over the breadth of human history to distinguish terrorism from war as even in the days of set peice battles there was foraging, looting, and raping often taking place. I think in the end if your side does it it's war and if the other side does it it's terrorism.
lfen