Complex sentence: Tobacco consumption in New Zealand peaked in the mid 1970s when 60% of the population where smokers, by 2011 that number had fallen to 20% of the population, thanks due to stringent tobacco control laws which are amongst the world's strictest.
Split into simpler sentences: Tobacco consumption in New Zealand peaked in the mid 1970s when 60% of the population where smokers. By 2011 that number had fallen to 20% of the population, thanks to stringent tobacco control laws which are amongst the world's strictest.