 As the northern tribal lands gradually opened to white settlement, Indiana's population rapidly increased and the center of population shifted continually northward.One of the most significant post-frontier events in Indiana occurred in 1818 with the signing of the Treaty of St. Mary's at St. Mary's, Ohio to acquire Indian lands south of the Wabash from the Delaware and others.The area comprised about 1/3 of the present day area of Indiana, the central portion, and was called the "New Purchase".