The plains of Oklahoma were filled primarily with shortgrass and tallgrass prairies, with wetlands, bottomland forests and savannas mixed in throughout. As such, the native prairie vegetation was very rich, and very fertile, a characteristic that attracted many farmers when westward expansion boomed in the United States.
Southern Oklahoma was primarily set aside in 1834 for the relocation of native peoples. Oklahoma eventually accommodated 67 tribes.
Due to its fertile soil and interspersed waterways, the promise of agricultural success attracted many Anglo-Americans to settle in Oklahoma beginning in 1889. In 1890, the Organic Act established Oklahoma Territory from former native lands, incorporating the Panhandle region into the newly established territory. Oklahoma and native territories together became the 46th State in the United States of America in 1907.
Cotton was a mainstay of the Oklahoma agricultural economy, but otherwise the state was split with large-scale wheat and grain in the northern to northwestern part of the state, and mixed and livestock raising in the rest of the state.
Other than agriculture, oil was a significant part of the Oklahoma economy. By 1901, Tulsa was the "Oil Capital of the World," ushering the petroleum industry into the 20th century.
J. J. Patton and R.A. Marston, The Encyclopedia of Oklahoma History and Culture, s.v. "Great Plains", https://www.okhistory.org/publications/enc/entry.php?entry=GR015