Because people back then were very superstitious <span />
By the late 1960s, people were declaring that “Lake Erie is dead.” The lake was heavily polluted with factory pollutants and sewer waste. ... As pollutants increased in the water, so did phosphorus and nitrogen levels, which led to the development of algal blooms.
Mass production of steel, large suspension bridges, steel frame construction in buildings. It allowed impurities to be removed cheaply and easily, enabling steel to be produced in mass quantities.
<span>According to William H. McNeill, one way the plague affected China after 1331 was that it reduced the population drastically and led to economic depression. </span>
