Complex sentence: Mahlon Dickerson, who was New Jersey's 12th Governor, and his family owned the Dickerson Mine, which was the largest ore mine in the area, supplying much of the iron ore used during the American Revolutionary War.
Split into simpler sentences: Mahlon Dickerson, who was New Jersey's 12th Governor, and his family owned the Dickerson Mine. It was the largest ore mine in the area, supplying much of the iron ore used during the American Revolutionary War.