It's been a long slow process to control the profession. But it could all be cracked open at one place: the ACGME, or Association for Collegiate Graduate Medical Education. They set the quotas every year on incoming students. They did a hostile takeover (called it a merger) of the osteopath accreditation board, as osteopaths used to be an escape from AMA allopathic medicine. They set the match (which is itself exempt from antitrust law by an act of congress) to control residencies, but the ACGME is not exempt from antitrust legislation. Any large state could also break their hold by licensing doctors differently, but they are trapped by preconceived notions, i.e. cowardice. I've done a lot of research on it. Many doctors hate them, but once they're through the gauntlet of obtaining their license they are happy to never look back at them again. Lots of doctors are ditching the insurance and allopathic models and going cash-only, but they are enslaved by huge debt, and very expensive as a result.