It is difficult to establish precisely when the League of the five Iroquois nations was founded and this determination is related to the purpose of the confederation. Was it a reaction to European contact or a much older indigenous form of organization?
Some scholars believe that the League could only have been formed after Europeans appeared. For example, Peter Farb argues, “An impetus for Iroquois confederation more likely than any vision of a prophetic Dekanwidah may be traced to the first probings by French ships into the Gulf of St. Lawrence, early in the sixteenth century” (Farb 1978: 90). But most suggest the League was formed sometime in the fifteenth century, well before the arrival of Europeans.
Specifically, most accounts place the founding of the Iroquois League between 1000 and 1450 CE, and the weight of the evidence seems to argue for the later date. Arthur Parker and Francis Jennings suggest that the League was formed in 1390 (Parker 1916: 71; Jennings 1993: 77), while Anthony Wallace thinks it happened around 1450, “in a successful endeavor to revive an even more ancient but less formally constructed ethnic confederacy” (Wallace 1970: 41-42). Some Iroquois accounts place the founding of the League one or two generations before the Iroquois first came in contact with Europeans: the French explorer Cartier first encountered Mohawk along the Saint Lawrence in 1534-5 (Tooker 1978a: 420-21). As William Fenton argues, “It is certain, however, that the League was founded before European settlement, probably about 1500 CE give or take 25 years, although arguments for earlier and later dates abound” (Fenton 1985: 16). This would be consistent with archaeological evidence that suggests the founding of the League was “sometime in the late fifteenth century” (Richter 1992: 31). Further, Iroquois oral traditions recall that the final negotiations for the League occurred during a time of a solar eclipse, which would put the founding around 1451 (Tooker 1978a: 420).
In sum, it seems likely that the League of the Iroquois was formed well before the five original nations came into contact with European explorers and settlers, although as Fenton notes, it was “an evolving institution” (Fenton 1985:16). The negotiations for the formation of the League were probably concluded around 1450, about 85 years before the Mohawks, in the League members’ first direct contact with Europeans, met Cartier on the Saint Lawrence. The Seneca nation was the last of the original five nations to decide to join. It appears that other Native nations were asked to join the League upon its formation, notably the Cherokee, Erie, and Delaware, but they declined (Parker 1916: 79-80 and 96).