The 1779 Sullivan Expedition was a United States military campaign during the American Revolutionary War, lasting from June to October 1779, against Loyalists and the four British allied Nations of the Iroquois. The campaign was ordered by George Washington, in response to the 1778 Iroquois–British attacks on Wyoming, German Flatts, and Cherry Valley, with the aim of "taking the war home to the enemy to break their morale". The Continental Army carried out a scorched-earth campaign, chiefly in the lands of the Iroquois Confederacy (also known as the Longhouse Confederacy) in what is now Pennsylvania and western New York state.

The expedition was largely successful, with more than 40 Iroquois villages and their stores of winter crops destroyed, breaking the power of the Iroquois in New York all the way to the Great Lakes. The campaign drove 5,000 Iroquois to Fort Niagara seeking British protection. With the military power of the Iroquois vanquished, the campaign depopulated the area for post-war settlement and opened up the vast Ohio Country, the Great Lakes region, Western Pennsylvania, West Virginia, and Kentucky to post-war settlements. Historians Rhiannon Koehler, Jeffrey Ostler, and Barbara Alice Mann argue that it was an attempt to annihilate the Iroquois and describe the expedition as a genocide, although this term is disputed, and it is not commonly used. Historian Fred Anderson, describes the expedition as "close to ethnic cleansing" instead. Today this area is the heartland of Upstate New York, with thirty-five monoliths marking the path of Sullivan's troops and the locations of the Iroquois villages they razed dotting the region, having been erected by the New York State Education Department in 1929 to commemorate the 150th anniversary of the expedition.