The 45-mile drive from Washington, D.C., to the quiet equestrian haven of Middleburg, Va., overflows with the sagas of America’s past. Crossing the Potomac River (where General Robert E. Lee’s troops fled after the Battle of Gettysburg), and bypassing signs for Spotsylvania Courthouse (the site of one of the Civil War’s bloodiest battles) and Fredericksburg (where Confederate forces blocked the Union army’s crossing of the Rappahannock River), the region is a living textbook of US history. Set against this ver…