Complex sentence: At Harpers Ferry, Ashby was assigned to the Virginia Militia command of ColonelThomas J. "Stonewall" Jackson and was responsible for guarding fords across the Potomac River and bridges from Harpers Ferry to Point of Rocks, Maryland.
Split into simpler sentences: At Harpers Ferry, Ashby was assigned to the Virginia Militia command of ColonelThomas J. "Stonewall" Jackson. He was responsible for guarding fords across the Potomac River and bridges from Harpers Ferry to Point of Rocks, Maryland.