There was a federal ban on sports betting in the USA from 1992 to 2018 under the Skilled and Amateur Sports Protection Act (PASPA).

The 1992 law allowed immunity to four countries that had previously permitted sports gambling inside their boundaries. Those states are Nevada, Delaware, Oregon, and Montana.
The state of New Jersey challenged the legality of PASPA. The Supreme Court heard oral arguments in late 2017. On May 14, SCOTUS issued a decision reversing the ban, striking down PASPA in total by a vote of 6-3. Due to the conclusion, the following countries now offer legal sports gambling:
Delaware — Launched June 5, 2018
Sports Betting at New Jersey — Launched June 14, 2018
Mississippi — Launched Aug. 1, 2018
West Virginia — Launched Aug. 30, 2018
Sports Betting in Pennsylvania — Launched Nov. 16, 2018
Rhode Island — Launched Nov. 26, 2018
Arkansas — Launched July 1, 2019
Countries that have passed sports gambling legislation, but have not found it yet:
Tennessee — April 30, 2019
Montana — May 3, 2019
Indiana — May 8, 2019 (get a full FAQ here)
Iowa — May 13, 2019
Illinois — June 2, 2019
Delaware was really the first into the enlarged marketplace. The nation used the existing sports gambling law on its books, based single-game wagering regulations, and began taking stakes on June 5, 2018.
A property in New Mexico also began booking legal wagers on Oct. 16. Santa Ana Star Casino & Hotel signed a deal with USBookmaking in early October to establish a sportsbook.
Why is New Mexico an interesting situation is that Santa Ana is a tribal home. Mississippi was the first nation to start tribal sports betting, but it was performed in tandem with a state law. In Santa Ana’s case, sports gambling is still prohibited elsewhere in the state, but the tribe can accept stakes on its land.
The Pueblo of Santa Ana Gaming Regulatory Commission regulates the casino wagers.

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