Stephen joined the provincial troops in 1754, and became lieutenant colonel of the Virginia Regiment under George Washington. The unit was based at Winchester (east of the Appalachian Mountains and the county seat of then-vast Frederick County), then explored westward across the Appalachian Mountains. It also fought native Americans, including battles at Jumonville Glen and Fort Necessity (both in 1754 and which some consider the opening engagements of the French and Indian War). The following year, Washington, Stephen and the Virginia militia participated in the disastrous Braddock Expedition. In 1756, Stephen led Virginia militiamen against the Creeks to relieve colonists from South Carolina. By 1759, Stephen was in command of at Fort Bedford (on the west side of the Appalachian range near the South Branch of the Potomac River) and begged for cattle to be delivered to Fort Pitt (the future Pittsburgh).