Date: June - September, 1779
The Sullivan Expedition was Washington's response to several raids by British and Iroquois groups along the northern frontier. Forces under Joseph Brant and John Butler had attacked forts and settlements in the Wyoming and Cherry valleys - killing and scalping women and children as well as militia.
Washington's orders were very clear. In order to root out the problem, Sullivan was to attack and burn as many Iroquois settlements as he could find, and take as many prisoners as he could. Sullivan complied, burning 40 Iroquois villages, and destroying an estimated 160,000 bushels of corn. His troops also answered previous atrocities with their own - scalping bodies, and burning people alive in cabins. Sullivan didn't limit his troops to active enemies, either - he also attacked the Onondaga, who had stayed neutral during the war. (This attack had the unsurprising effect of making the Onondaga into enemies of the Patriots.)
In the end, the Sullivan expedition failed to stop raids in the area - those continued throughout the revolution, as each side sought to get revenge for the violence of the other. The repeated attacks on both sides eventually laid waste to the entire Kanièn:keh Territory (also known as Mohawk Valley) and the land around it.
Possibly because of the Sullivan Expedition, George Washington became known among the Iroquois as the "Town Destroyer". Although, the origin of the nickname is historically contested - he might have already earned it destroying towns during the French and Indian war. Now there's the mark of a great statesman - it's hard to tell when he got a reputation for scorched earth policies, because he did it so much.