The Territory of Oklahoma was an organized incorporated territory of the United States that existed from May 2, 1890, until November 16, 1907, when it was joined with the Indian Territory

Indian Territory

The Indian Territory, also known as the Indian Territories and the Indian Country, was land set aside within the United States for the settlement of American Indians...

 under a new constitution and admitted to the Union

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 as the State of Oklahoma.
Oklahoma Territory's history began with the Indian Intercourse Act

Indian Intercourse Act

The Nonintercourse Act is the collective name given to six statutes passed by the United States Congress in 1790, 1793, 1796, 1799, 1802, and 1834. The Act regulates commerce between Native Americans and non-Indians...

 of 1834 when the United States Congress

United States Congress

The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....

 set aside land for Native Americans. At the time, the land was unorganized territory

Unorganized territory

An unorganized territory is a region of land without a "normally" constituted system of government. This does not mean that the territory has no government at all or that it is unclaimed territory...

 that consisted of all the federal land "west of the Mississippi and not within the states of Missouri and Louisiana, or the territory of Arkansas..." By 1856, the territory had been reduced to the modern-day borders of the State of Oklahoma.