From 1890 until Oklahoma statehood in 1907, the term "Twin
Territories" was used to refer to Oklahoma and Indian
territories. Most of present Oklahoma was called Indian
Territory in the early 1800s. Indian Territory was primarily the
home of the Plains Indians until the Five Civilized Tribes were
relocated there in the first half of the nineteenth century. The
domain of the Five Civilized Tribes was reduced to approximately
the eastern half of present Oklahoma by the Reconstruction
Treaties of 1866. In 1889 the Unassigned Lands in the central
part of present day Oklahoma were opened for non-Indian
settlement and called Oklahoma Territory by the Organic Act
(1890). Following allotment in severalty by American Indians,
Oklahoma Territory expanded primarily by opening unallotted land
to settlers through other land runs, a lottery, and an auction.
As additional areas such as the Oklahoma Panhandle and Greer
County were added by the federal government in 1890 and 1896,
respectively, Oklahoma Territory would eventu