Complex sentence: Manchester's Amoskeag Mills was once the largest cotton textile plant in the world and other major textile companies based in the Merrimack Valley cities include the Merrimack Manufacturing Company in Lowell, Pemberton Mill in Lawrence and the Nashua Manufacturing Company in its namesake city.
Split into simpler sentences: Manchester's Amoskeag Mills was once the largest cotton textile plant in the world. Other major textile companies based in the Merrimack Valley included the Merrimack Manufacturing Company in Lowell, Pemberton Mill in Lawrence and the Nashua Manufacturing Company in its namesake city.