Phelps and Gorham Purchase

The Phelps and Gorham Purchase was the 1788 sale by the state of Massachusetts of its preemptive right to a portion of a large tract of land in western New York State owned by the Seneca nation of the Iroquois Confederacy to a syndicate of land developers led by Oliver Phelps and Nathaniel Gorham. The larger tract of land is generally known as the "Genesee tract" and roughly encompasses all that portion of New York State west of Seneca Lake, consisting of about 6,000,000 acres (24,000 km2).

Source: Wikipedia — Phelps and Gorham Purchase (CC BY-SA 4.0)