During the American Revolution, the British base at Fort Niagara served as a safe haven for those loyal to the British, whether European settlers or Haudenosaunee villagers, and a base for offensive operations against colonial settlements on the frontier.
Combined colonial and Native American forces organized at Fort Niagara conducted raids against colonial settlements in the Mohawk Valley and northeastern Pennsylvania, their former neighbors, in an escalating cycle of violence and atrocities.
Active participation by most Haudenosaunee tribes on the British side and some on the American side through raids on the frontier led to the targeting of their villages in central New York by American forces. As a result of the war, the Six Nations were divided, with some moving to Ontario and others staying in New York; the Tuscarora fought on both sides of the Revolutionary War. Post-war treaties shrank Haudenosaunee lands to a few scattered reservations, opening Western New York for settlement by Europeans.
The Niagara River, as is the entire Great Lakes Basin of which the river is an integral part, is a legacy of the last Ice Age. 18,000 years ago southern Ontario was covered by ice sheets 2-3 kilometers thick.