In a stunning blow to Oklahomas state government, the U.S. Supreme Court ruled Thursday that much of eastern Oklahoma is located on an Indian reservation.

In a 5-4 ruling , the justices declared that Congress never diminished or disestablished the land as a reservation. Major crimes committed by a tribal member on their own reservation, in effect, must be prosecuted by the federal government in accordance with the Major Crimes Act. This could open the door to numerous appeals by people prosecuted by the state of Oklahoma who should have been under tribal jurisdiction.

The opinion was also an acknowledgment by the nations highest court that the U.S. government has, time and time again, broken promises to Indian tribes. The Supreme Courts opinion means that at least for the matter of this land, the government must keep its commitment.

Today we are asked whether the land these treaties promised remains an Indian reservation for purposes of federal criminal law. Because Congress has not said otherwise, we hold the government to its word, Justice Neil Gorsuch wrote in the majority opinion.

While there can be no question that Congress established a reservation for the Creek Nation, its equally clear that Congress has since broken more than a few of its promises to the Tribe, he wrote. Not least, the land described in the parties treaties, once undivided and held by the Tribe, is now fractured into pieces.

The Muscogee (Creek), Cherokee, Choctaw, Seminole and Chickasaw Nations which make up the Five Civilized Tribes were hoping for a ruling that would uphold their sovereignty and the status of their lands as reservations, which currently make up around 19 million acres and nearly the entire eastern half of Oklahoma, including much of Tulsa.

As white colonizers moved West, they forced Indigenous people from their lands and onto reservations across the U.S. Eventually, Native Americans were even forced off their original reservations as colonizers continued to settle and did not want to live among Indigenous people. The debate over who has authority over the eastern part of Oklahoma is in line with that long-running conflict.

The Supreme Court reaffirmed today that when the United States makes promises, the courts will keep those promises, Ian Heath Gershengorn, who argued a related case before the Supreme Court, said in a statement. Congress persuaded the Creek Nation to walk the Trail of Tears with promises of a reservation and the Court today correctly recognized that this reservation endures.

The tribes and the state of Oklahoma have been waiting on a decision on the matter for years.

The court punted on the matter last year when it failed to come to a decision in Sharp v. Murphy , the case Gershengorn argued. That case involved Patrick Murphy, a member of the Muscogee (Creek) Nation who is on death row for murder. The court sought to establish whether land within the 1866 territorial boundaries of the Creek Nation in eastern Oklahoma, formerly known as Indian Territory, could still be considered an Indian reservation. But the court failed to settle the case, with only eight justices participating in the deliberations. Gorsuch recused himself because of his involvement in the 10th Circuit Court of Appeals, which ruled on the matter previously.

The McGirt case gave the court another opportunity to consider tribal boundaries and sovereignty. More than two decades ago, Jimcy McGirt was convicted in Oklahomas Wagoner County District Court of lewd molestation, first-degree rape and forcible sodomy. He was sentenced to 500 years each for the rape and molestation counts and to life without parole for the forcible sodomy charge.

McGirt argued that as an enrolled member of the federally recognized Seminole and Muscogee (Creek) Nations, the state of Oklahoma could not prosecute him, according to the Major Crimes Act of 1885. That law states that the federal government alone has the authority to prosecute any major crime committed by an enrolled member of a tribe on their own reservation.

McGirts legal team argued that the Major Crimes Act of 1885 qualified McGirt for an appeal because the state government had no jurisdiction to prosecute him in the first place. Instead, his lawyers argued, McGirt should have been prosecuted in federal court.

Eventually, the case made its way to the Supreme Court, which heard oral arguments on May 11 via teleconference due to the coronavirus pandemic.

The oral arguments centered around whether the Creek Nation ever had a reservation and, if so, if it was ever disestablished. Federal Indian reservations are usually exempt from state jurisdiction since Native American tribes have the right to govern their own internal affairs. The Constitution gives the federal government, not state governments, the authority to deal with tribes as governments.

In both the Murphy and McGirt cases, petitioners argued that Congress never disestablished their tribal reservations or changed their boundaries and that those lands are still reservation land. That means that the men in question should be prosecuted by federal courts and not the state.

The state of Oklahoma, meanwhile, argued that those lands were Dependent Indian communities and not reservations. This would disqualify them from being considered a reservation and mean that the state had the authority to prosecute the mens cases.

Supreme Court Chief Justice John Roberts, along with Justices Samuel Alito, Brett Kavanaugh and Clarence Thomas, sided with the state.

In the dissenting opinion, Roberts said the courts ruling will have major consequences for the areas residents, who are largely not part of any tribe, and state laws, including those pertaining to zoning, taxation, family and environmental law.

The rediscovered reservations encompass the entire eastern half of the State19 million acres that are home to 1.8 million people, only 10%15% of whom are Indians, he wrote. Across this vast area, the States ability to prosecute serious crimes will be hobbled and decades of past convictions could well be thrown out. On top of that, the Court has profoundly destabilized the overnance of eastern Oklahoma.

Roberts went on to argue that Congress did disestablish Indian territory by dismantling tribal governments, tribal courts and tribal sovereignty, as well as by making the tribal members U.S. citizens.

In taking these transformative steps, Congress made no secret of its intentions. It created a commission tasked with extinguishing the Five Tribes territory and, in one report after another, explained that it was creating a homogenous population led by a common government, he wrote.

Sen. Ted Cruz (R-Texas) had a more direct statement of opposition to the opinion making clear that he viewed the decision as taking away land from Oklahoma, rather than an acknowledgment that it wasnt Oklahomas to begin with.

Neil Gorsuch & the four liberal Justices just gave away half of Oklahoma, literally, Cruz tweeted. Manhattan is next.

But legal experts said the opinion, though important, would not wreak the kind of instant havoc detractors warned about.

In a joint statement, the State of Oklahoma, Muscogee (Creek), Cherokee, Chickasaw, Choctaw, and Seminole Nations said they will work together to move forward after the Supreme Courts decision.

The Nations and the State are committed to implementing a framework of shared jurisdiction that will preserve sovereign interests and rights to self-government while affirming jurisdictional understandings, procedures, laws, and regulations that support public safety, our economy, and private property rights, the statement read. We will continue our work, confident that we can accomplish more together than any of us could alone.

The decision could change how many things operate on tribal lands, but not instantaneously, according to Forrest Tahdooahnippah, a member of the Comanche Nation of Oklahoma and a lawyer who specializes in businesses in Native American country.

In the long term, outside of the criminal context, there may be some minor changes in civil law, the majority opinion points out assistance with homeland security, historical preservation, schools, highways, clinics, housing, and nutrition programs, as possible changes. The Creek Nation will also have greater jurisdiction over child welfare cases involving tribal members, Tahdooahnippah said. The short term implications of McGirt are largely confined to the criminal context in which the case arose.

He added that individuals convicted by the state may not want to challenge their convictions again. Federal penalties may be harsher than the state penalties, he said.

Lindsay Robertson, Chickasaw Nation Endowed Chair in Native American Law at the University of Oklahoma College of Law, said this advancement to sovereignty will not be a process that happens overnight that some have feared may overwhelm the court system.

This is doable because everybody the tribes and the state has the same goals: law and order, preservation of peace, economic advancement and this sort of thing, Robertson told HuffPost.

Robertson said the short-term implications will definitely include the court receiving many petitions for appeals.

I think it is likely that some will file today; I would be surprised if some criminal defense lawyers didnt file petitions to have their clients released from state prison today.