The court decided 5-4 that an eastern chunk of the state, including its second-biggest city, Tulsa, should be recognized as part of a reservation.

Written by Justice Neil Gorsuch, the ruling means Oklahoma prosecutors now lacks the authority to pursue criminal cases against Native American defendants in large parts of Oklahoma.

This ruling is seen as one of the most important legal victories for Native Americans in decades and could have far-reaching implications for the people who live in Oklahoma, particularly those who live in what the court yesterday affirmed was Indian Country.

The ruling also casts doubt on hundreds of convictions won by local prosecutors. It means some tribe members found guilty in state courts for offenses committed on the land can now challenge their convictions.

In The New York Times, Principal Chief David Hill said that it was a historic day. “This is amazing. It’s never too late to make things right,” Hill said.

The Principal Chief’s thoughts were echoed by many on social media, who celebrated the decision with the declaration, “Native Lives Matter.”

However, Chief Justice John G. Roberts Jr. warned the court’s decision would cause great damage to Oklahoma’s criminal justice system, saying: “The state’s 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 governance of eastern Oklahoma.”

The Chief Justice’s comments came after the Justice Department raised concerns about how federal prosecutors would cope with the new cases they would be suddenly responsible for investigating.

Meanwhile, as per The Guardian, Justice Neil Gorsuch suggested optimism. “It is unclear why pessimism should rule the day. With the passage of time, Oklahoma and its Tribes have proven they can work successfully together as partners.”

Oklahoma’s three US attorneys released a joint statement after the ruling, expressing confidence that ‘tribal, state, local and federal law enforcement will work together to continue providing exceptional public safety’.