William H. McNeill, a world historian, noted in chapter three of his book "Plagues and Peoples" (1976) that the Roman Empire suffered the severe and protracted Antonine Plague starting around 165 AD. For about twenty years, waves of one or more diseases, possibly the first epidemics of smallpox and measles, swept through the Empire, ultimately killing about half the population. Similar epidemics, such as the Plague of Cyprian, also occurred in the 3rd century. McNeill argues that the severe fall in population left the state apparatus and army too large for the population to support, leading to further economic and social decline that eventually killed the Western Empire. The Eastern half survived due to its larger population, which even after the plagues was sufficient for an effective state apparatus.