The Five Nations of the Iroquois Confederacy settled into the area that is now Upstate New York about 1200 CE, with the related Tuscarora joining them from the Carolinas around 1720, increasing the number of allied tribes to six. They called themselves “Haudenosaunee,” meaning “The People of the Longhouse.” Though their men ranged wide and far for both hunting and war expeditions, the Iroquois were far from nomadic, being settled in well-established towns.
The Mohawk, inhabiting lands near the conjunction of the Mohawk and Hudson Rivers, guarded the eastern approaches to the Iroquois heartland. The Seneca, living in regions now close to the city of Buffalo, protected the western borders. Oneida inhabited the upper Mohawk Valley; Cayuga were centered on the Finger Lakes; Onondaga kept the Council fire near present day Syracuse. The Tuscarora settled south of the Oneida, mostly between the Oneida and the current New York – Pennsylvania border.
By the early 18th Century, Iroquois interests dominated much of the Ohio, Hudson, Delaware, Susquehanna, Chenango, Mohawk, and upper St. Lawrence River valleys. They had both significant influence and imperial designs on the territories in between and bordering this region.
Confederacy control of the Mohawk River Valley, which provided a large water level route connecting North America’s East Coast and the lands on the western side of the Appalachian Mountains, positioned the Iroquois well for hegemony.
The Iroquois generally had balanced French, Dutch, and English colonial efforts to their own advantage. The Confederacy effectively ended French plans to expand colonial holdings using Huron allies in 1649, and was crucial to the victory of England and its colonists in the French and Indian War [1754 – 1763]. The Iroquois were equally astute in the subsequent peace negotiations, protecting their lands in part by increasing the real estate holdings of the British Superintendent of Indian Affairs, Sir William Johnson.
Sir William Johnson was yet another of those meteoric Irishmen who carved such spectacular careers through the 18th and 19th centuries. After he arrived in North America, he immersed himself in Indian culture, going native to the point that he was adopted into the Mohawk Nation. He commanded Iroquois and militia troops during the French and Indian war, and was fortunate enough to be available for the honor when the English decided they needed a hero after the Battle of Lake George . He provided substantial service in the capture of Fort Niagara  and the assault on Montreal .
While protecting Iroquois territory from westward pushing colonials, Johnson accumulated vast personal land holdings [about 170,000 acres, 690 square kilometers]. He was fiercely loyal to Britain, and convinced many of his native allies that they should be so as well. He died on the 11th of July in 1774 while hosting a meeting of representatives of the Iroquois Confederacy, but his baneful influence lived on. His lands were confiscated after the American Revolution.
At the opening of the American Revolution, which they correctly saw as a sort of civil war, the Six Tribes tried without success to remain neutral. Many Oneida and Tuscarora allied themselves with the American revolutionaries. The Mohawks, Onondaga, Cayuga and Seneca generally sided with the English.
British-allied Iroquois warriors were effective raiders against civilian populations and isolated militias. They gained well deserved notoriety with massacres in Wyoming [Pennsylvania] in July 1778 and Cherry Valley [New York] in November 1778. The former inspired Thomas Campbell’s romantic epic in Spenserian stanzas, Gertrude of Wyoming , which was well reviewed at the time of its publication, despite its many historical errors.
Loosing aboriginal warriors on settlers of European descent was the nuclear option of its day. It did not ultimately work for the French, however, and was counterproductive for the English. The 1778 raids on the frontier caused George Washington to order the Sullivan – Clinton expedition to carry out a scorched earth policy in the Iroquois heartland in the summer of 1779.
There was only one major battle. It took place near what is now Elmira New York on August 29th, 1799. Sullivan’s troops avoided stumbling into an ambush, and used artillery and sharply pushed infantry attacks to completely rout the British and their Iroquois allies. About a dozen died on each side of the battle. Plausible but unproven hypotheses suggest that two senior Iroquois political chieftains, one a woman, may have been killed while observing the fighting. More importantly, Sullivan’s forces were essentially unopposed when they subsequently dismantled the heart of the Iroquois economy by destroying more than 40 villages, including food reserves and crops in the field.
The expedition’s leaders, Generals John Sullivan and James Clinton, were severely criticized at the time for not exterminating the Iroquois warriors, who raided the frontier the next two summers. But the power of the Iroquois Confederacy had been permanently broken. The Iroquois death toll from exposure and starvation far outnumbered battlefield casualties. Many died during the winter of 1779 – 1780 outside of Fort Niagara, where in a curious echo of the French managed starvation of the Hurons on Christian Island [1649 – 1650], the British proved strikingly incapable of providing food and shelter for their refugee allies. It proved impossible for the tribes to recover from the destruction of their settlements in the Iroquois heartland.
The Treaty of Paris ended fighting between the American revolutionaries and England in 1783. A peace treaty with the Iroquois was not signed until the following year. This treaty formalized the loss of a great deal of the Confederation’s land. Much of the remainder was stolen by white settlers afterwards. The American allies among the Oneida and Tuscarora were treated nearly as badly as the tribes who fought against the revolutionary Americans.
• Francis Jennings’ The Ambiguous Iroquois Empire is a good place to start investigating Iroquois history.
• Barbara Graymont’s The Iroquois in the American Revolution and Max Mintz’s Seeds of Empire: The American Revolutionary Conquest of the Iroquois provide overviews of the end of the Iroquois empire.