Beginning in the 1820s, the area that would become Kansas was set aside as Indian Territory by the U.S. government, and was closed to settlement by whites. The government resettled to Indian Territory (now part of Oklahoma) those Native American tribes based in eastern Kansas, principally the Kansa and Osage, opening land to move eastern tribes into the area. By treaty dated June 3, 1825, 20 million acres (81000 km2) of land was ceded by the Kansa Nation to the United States, and the Kansa tribe was limited to a specific reservation in northeast Kansas. In the same month, the Osage Nation was limited to a reservation in southeast Kansas.