He pursued two intertwined interests: military arts and western expansion. At 16 he helped survey Shenandoah lands for Thomas, Lord Fairfax. Commissioned a lieutenant colonel in 1754, he fought the first skirmishes of what grew into the French and Indian War. The next year, as an aide to Gen. Edward Braddock, he escaped injury although four bullets ripped his coat and two horses were sh ot from under him. Which is the central idea in this excerpt?