Prior to the arrival of Europeans, the land area around Western New York State and Northwestern Pennsylvania was populated by the Seneca Nation of the League of the Iroquois. The League was a confederacy which united various speakers of the Iroqouis language (the Senecas, Mohawks, Oneidas, Onondagas, Cayugas, etc.) throughout New York State and into Pennsylvania. The Senecas at that time were the largest and most powerful of all the Iroquois Nations, and were the furthest west of all the Nations, considered guardians of the "western door" by the League. In the mid-seventeenth century, the Senecas fought with a small tribe known as the Eries, which dwelled along Lake Erie. The defeat of the Eries, in a battle where French Creek joins the Allegheny River, opened the French Creek area to Seneca settlement, where they remained for many years. The Pymatuning region (to the west) remained neutral ground between the Senecas and the Shawnees.
The Seneca interacted with the French as they built their forts at present-day Erie, Waterford, Franklin, and Pittsburgh. But when the French and Indian War finally broke in the early 1750's, a split of sorts occurred within the Iroquois Confederacy. Because the French had not "settled" the land within the Seneca area as the British hoped to, the Seneca felt they had no choice but to support the French in the War. The Oneidas and Mohawks supported the British, and the Cayugas and Onondagas remained neutral. However, the Iroquois nations would not attack other Iroquois, and would just disappear if they happened to each show up for battle along with their French or British allies.
During the Revolutionary War, the Iroquois tried to remain neutral, but eventually sided with the British because they wanted American settlers off their land. The neutrality was officially ended at Oswego in July, 1777, after which they attacked the Americans at Fort Stanwix near Rome, New York. At this time, the Senecas were led by Kiasutha and his nephew, Cornplanter. Cornplanter distinguished himself as a heroic war chief during the Revolution, often engaged in battles with forces led by George Washington, for whom Cornplanter reportedly had great respect.
Following the War, when Cornplanter took over as Seneca Chief from his uncle, Cornplanter's respect for Washington only increased as they negotiated various land treaties between the Seneca and the new American government. In fact, Cornplanter negotiated one of the only lasting land treaties with the United States, and was even given land personally by the U.S. government. Because Chief Cornplanter and the Senecas held a domain that stretched from present-day Buffalo to Pittsburgh, and from Chautauqua Lake to Cleveland, the French Creek Valley existed inside of this area. For the most part, Cornplanter and his people existed in relative harmony with the American settlers, and even defended them against attack on several occassions. Conplanter, the leader of the Seneca Nation, died in 1836 at the age of 104. (Not all historians agree on his age at the time of his death.)
Although eventually treated harshly and forced out of most of the French Creek region by American military campaigns and broken treaties, the Seneca held influence there for many decades. In addition, the Seneca's social and political structure rivaled that of America's (in fact, many believe that the Iroquois Confederacy provided a model upon which much of the U.S. Constitution is based). Particularly, women held positions of high respect within Seneca society, and played major roles not only in family life, but also in shaping governmental decisions, settling disputes, and fostering community planning. The Iroquois also seemed to be much more accepting of other people than America has been historically. By most accounts, the Iroquois readily accepted European whites into their nations and families. In fact, Chief Cornplanter himself was half-Dutch, decended from a Seneca mother and a Dutch trader.