During their heights, many great empires were considered invincible - before God and Man. Ruling over great territories and thriving for centuries, such empires were major global powers, and invading them was never an option for a would-be enemy. And yet, even such great powers declined and crumbled, and often without the aid of an enemy. Because even the greatest of realms are helpless in the face of the invisible enemy - disease. In our distant past, when medicine was still in its infancy, disease and sickness was often rampant. And once it took hold, it spared no one and nothing that stood in its path. Empires included. Disease, the Greatest of Conquerors In ancient times, disease played a major role in the gradual decline of kingdoms, cities, and even vast empires. This is because major outbreaks of sickness further exacerbated the existing economic, social, and political issues. Of course, for most of history the causes for decline in power were usually warfare, repeated economic stress, and political instability. But often, such problems could have been dealt with, and power regained. With disease, however, there was no going back. Because disease decimated the population of an empire, strained its resources, and devastated the pre-existing social order. And without the people to put things right, how could an empire regain its power? Read moreSection: NewsGeneralScience & SpaceScienceEuropeAsiaAmericasHistoryImportant EventsPremiumPreviewRead Later