Complex sentence: The increased industrial use of Portland cement in the late 19th and early 20th centuries was detrimental to Rosendale's economy, and the village lost almost 70 percent of its population between 1900 and 1920; only one cement factory remained open after 1920.
Split into simpler sentences: The increased industrial use of Portland cement in the late 19th and early 20th centuries was detrimental to Rosendale's economy. Between 1900 and 1920 the village lost almost 70 percent of its population, and only one cement factory remained open after 1920.