Historically, the dawn of agriculture led to the rise of contagious diseases. Compared to their hunting-gathering counterparts, agrarian societies tended to be sedentary and had higher population densities, were in frequent contact with livestock, and were more exposed to contaminated water supplies and higher concentrations of garbage. Poor sanitation, a lack of medical knowledge, superstitions, and sometimes a combination of disasters exacerbated the problem. Journalist Michael Rosenwald wrote, "...history shows that past pandemics have reshaped societies in profound ways. Hundreds of millions of people have died. Empires have fallen. Governments have cracked. Generations have been annihilated."