Complex sentence: Since the early 1970s, the tobacco industry has been concerned about second hand smoking as a serious threat to its business interests; harm to bystanders was perceived as a motivator for stricter regulation of tobacco products.
Split into simpler sentences: Since the early 1970s, the tobacco industry viewed public concern over secondhand smoking as a serious threat to its business interests. Harm to bystanders was perceived as a motivator for stricter regulation of tobacco products.