Much as occurred in the original series, Romulans of the (non-canon) Star Fleet Universe descended from the Vulcans, having rejected the movement toward an unemotional, logic-based society, and settled in a distant star system.
After the General War, the Romulan Empire erupted in civil war, had their border stations destroyed by the Interstellar Concordium in the course of the ISC War of Pacification, and subsequently aided in resisting the extragalactic Andromedan invasion.