Complex sentence: Tilton remained in service with the Continental Army as the head of military hospitals, first at Princeton and later at Trenton, New Jersey and other sites; and when active fighting ended in 1781 he returned to his practice at Dover.
Split into simpler sentences: Tilton remained in service with the Continental Army as the head of military hospitals, first at Princeton and later at Trenton, New Jersey and other sites. When active fighting ended in 1781 he returned to his practice at Dover.