Complex sentence: By 1920 Chewelah's population had grown to 1,600 people, and the town continued to prosper until 1968, when the magnesite plant closed down due to cheaper competition from Japan and changes in the steel industry.
Split into simpler sentences: By 1920 Chewelah's population had grown to 1,600 people and continued to prosper until the late 1960's. In 1968 the magnesite plant closed down due to cheaper competition from Japan and changes in the steel industry.