Complex sentence: Major industries in Stockton have included ship building and repairing, heavy engineering as well as steel and chemicals manufacturing, however during the twentieth century the town's heavy industry declined dramatically, along with that of the surrounding Teesside area.
Split into simpler sentences: Major industries in Stockton have included ship building and repairing, steel and chemicals. During the twentieth century the town's heavy industry declined dramatically, along with that of the surrounding Teesside area.