This is not entirely correct.
Within the United States, each state has requirements for independent licensure as a physician. All states require a degree from an accredited school of medicine (allopathic or osteopathic or foreign) and passage of the United States Medical Licensing Exams, of which there are three (1, 2 is divided into a written and clinical portion, and 3). Some states require a year of training under the supervision of licensed physicians in an accredited training program (residency program). Many states require more (often at least 2 years). Completion of a residency program is not a requirement in most states. HOWEVER, most specialities also have certifying boards. These certifications are necessary to claim that you are practicing a particular specialty (from internal medicine to geriatrics to plastic surgery). These certifications, given by the national board of whichever specialty, uniformly require completion of an appropriate residency training program, possibly a fellowship training program, and passage of board exams administered by the specialty's certifying board.