I think the answer is the 10th Amendment
Oklahoma's economic history is divided into four periods. The first period covers the nineteenth century, encompassing settlement by American Indians of the Southeast followed by new arrangements facilitating private land ownership. The second extends from 1900 to the onset of the Great Depression in 1930. The third ends in 1973 with the first of the major oil shocks. The fourth comprises the energy boom and bust of the late twentieth century, along with contemporary conditions.
The century from 1800 to 1900 encompassed the time of Indian and white settlement. During the nineteenth century Oklahoma was characterized by very high ratios of land to labor and capital, by almost total dominance of primary (natural resource based) production, and by unique institutional and cultural features, of which the effects of some remain important in today's economy. The initial settlement by the Five Civilized Tribes in the 1820s, 1830s, and 1840s in what is now Oklahoma (at that time Indian Territory) did not reflect free-market labor migration in response to income differentials. Added to the coercion of removal was the fact that the Five Tribes had adopted the institution of slavery in their former southern setting. Slave-owning Indians brought with them an additional labor supply.
