##Indian Territory
Indian Territory was originally set up as a "dumping ground," so to speak, for Tribes that were removed from the southeastern region of the United States. It provided a location for many Tribes to be relocated to where the promises made to Tribes could be upheld because, at first, Indian Territory encompassed undesirable land and was beyond the immediate boundary for westward expansion (the Mississippi River). Originally, these lands were meant for the "Five Civilized Tribes:" the Cherokee, Seminole, Chickasaw, Choctaw, and Creeks. Their removal in the 1830s was secured via treaties that made very specific stipulations for their land holdings since they were being dispossessed of their homelands by force. These treaties had more rigid and defined terms that clearly outlined that the Big Five (a better name, IMO, than "Five Civilized Tribes") would own the land in perpetuity, it would be closed to all non-Indian settlement, and that these reservations "would never become part of a state without the tribe's consent."^1 Combined with the previously mentioned factors, Indian Territory would be virtually left alone for some time.
After the American Civil War, the United States Congress--the sole entity designated to have Plenary Power over Indian Tribes--penalized Tribes in this territory for politically sympathizing with the Confederacy. They transferred huge swaths of land (about half the territory) out of the control the Big Five, thus creating the Oklahoma Territory. Congress also began relocating many other Tribes further west to Indian Territory. It eventually looked like this (circa 1890s). Though reservations were created in the new Oklahoma Territory, these did not have as strict of rules governing them as established by treaties like Indian Territory did. Indian Territory remained closed for settlement and land sales, though this would soon change with the Allotment Era.
##Allotment
In 1887, the General Allotment Act (AKA The Dawes Act) was passed that broke up communal land holdings on reservations. Indian families were apportioned acreage within reservations and any land leftover was considered "surplus" and was available to be sold off at cheap prices for settlement by non-Indians--within reservation boundaries. But Indian Territory was different. The aforementioned Treaties resulted in much of the lands in Indian Territory and the Oklahoma Territory being exempted from allotment...until 3 years later.
Come 1898, Congress also passed the Curtis Act that subsequently "abolished all tribal courts and removed certain powers of self-government from the tribes, including the right to collect taxes" while also doubling down on the forced allotment of Tribal lands.^2 By 1906, 99% of the allotted territory within the Osage Reservation--an area with a landmass equaling 3% of the future state's territory--was owned by non-Indians.
Much like with all treaties, the United States broke the ones governing their relationship with the Tribes in Indian Territory. Land ownership by Indians rapidly decreased and more legislation saw that Tribes lost jurisdiction over these lands. A political power struggle developed between the settlers moving in clamoring for membership into the Union and the Indians wanting to preserve their sovereignty and ways of life.
##State of Sequoyah
Recognizing the impending downsize of their sovereignty and ability to exercise control within their territory, Tribal leadership within the rest of Indian Territory acted to abate this future. The Big Five were accustomed to utilizing and adopting Western ways. In 1905, a constitutional convention was held in Indian Territory to examine the potential of admitting Indian Territory into the Union as a state represented by Indian governing authorities.
Following the convention, the Sequoyah Constitution was presented to eligible voters and the measure was ratified by an overwhelming margin of 56,279 to 9,073. Approximately 75% of eligible voters participated in the election, including citizens of the Five Tribes and other U.S. citizens residing within Indian Territory in 1905 that had not previously established tribal citizenship.^3
Unfortunately, this measure would be defeated. President Teddy Roosevelt was against the idea of having two recognized political entities in the area and favored combining them into one state. His preference caused indifference to develop among the congressional support that Indian diplomats were seeking and the movement to create the State of Sequoyah dwindled. Even worse, this placed the Tribes in a precarious situation as they faced continued land and political dispossession. Many feared that their Tribal governments would soon cease to exist as polities and the federal trust relationship with these Tribes would be terminated, leaving them to be further assimilated into American society. Though this movement failed, it did demonstrate the resolve of Indian leaders to secure their future.
Primarily for partisan political reasons, Sequoyah was never admitted to the Union. The Burke Act in 1906 specifically extended and preserved the existence and sovereignty of the Indian Tribes that would have become the heart of the State of Sequoyah. The final congressional act in a series drawing an end to the Indian Territory continued indefinitely the rights and powers of tribal government as they now exist in Oklahoma using the following specific words:
The Tribal existence and present Tribal governments of the Choctaw, Chickasaw, Cherokee, Creek and Seminole Tribes or Nations are hereby continued in full force and effect for all purposes authorized by law, until otherwise provided by law.
On June 16, 1906, the Republican President, Theodore Roosevelt, no longer fearful of Sequoyah as a Democrat State, signed the Enabling Act which opened the way to the single Statehood of Oklahoma in 1907.^4
Though this was obviously not the preferred option, this route allowed the Tribes of Indian Territory to preserve their existence even after Oklahoma was admitted as a non-Indian state into the union. And despite the slightly different relationship Tribes in Indian Territory shared with the federal government, the Tribes were considered under the same umbrella patchwork of federal Indian policy as all other Tribes in where the treaties continued to be recognized unless abrogated by Congress (cough same goes for reservations, if we wanna talk about some recent land jurisdiction being given back cough). Sadly, the passage of time would result in the erosion of Tribal sovereignty in practice in Oklahoma where lack of federal oversight and continued political attacks by settlers found much of the existing reservation boundaries being ignored and, in a de facto sense, erased.
One of the most substantial obstacles the Five Tribes had to overcome, and are still addressing today, is the ill-conceived perception of the Oklahoma leaders and the general public. Although lacking in legal authority, Oklahoma leaders presumed that the governments of the Five Tribes went out of existence with the advent of Oklahoma and that the reservation boundaries failed to survive statehood. Although this viewpoint is inconsistent with the Oklahoma disclaimer clauses, and multiple court cases, it is well-rooted in Oklahoma folklore and is still a widely held assumption today.^5
##Conclusion
With mounting political pressure and land dispossession via allotment, Indian Territory was faced with Manifest Destiny. Teddy Roosevelt was certainly not a fan of Indians (look to his infamous quote on his feelings toward "10 Indians") and saw political pitfalls by admitting an Indian state to the Union. Gradual erosion of expressed Tribal sovereignty and loss of congressional support meant that there was little recourse for the Tribes of Indian Territory and a lack of consequence for the United States by ignoring the movement for Sequoyah. Eventually, it became inconsequential and Oklahoma, the non-Indian bred territory, was admitted to the Union in 1907.
Edit: Words and added some additional linked resources.
Footnotes
[1] Stephen L. Pevar, Rights of Indians and Tribes, 4th edition (New York: University of Oxford Press, 2012), 265.
[2] Pevar, Rights of Indians and Tribes, 266.
[3] Stacy L. Leeds, "Defeat or Mixed Blessing - Tribal Sovereignty and the State of Sequoyah," Tulsa Law Review 43, no. 1 (Fall 2007): 6.
[4] Rennard Strickland, "Sequoyah Statehood, the Oklahoma Centennial and Sovereignty Envy: A Personal Narrative and a Public Proposal," American Indian Law Review 30, no.2 (2006): 366-367.
[5] Leeds, "Defeat or Mixed Blessing," 11.