Complex sentence: In 2005, the IAO became a member of the Osteopathic International Alliance (OIA), an organization that advances the philosophy and practice of osteopathic medicine and osteopathy worldwide.
Split into simpler sentences: In 2005, the IAO became a member of the Osteopathic International Alliance (OIA). The OIA is an organization that advances the philosophy and practice of osteopathic medicine and osteopathy worldwide.