Over the course of 250 years, Rome's population dropped from about 65 million to 50 million. Historians call this period of time the 'Dark Ages'. Some people believe this was because of a global cold front that swept the earth. The Romans slowly lost their control of the empire as other, stronger groups moved through the area. There were many battles, and the Romans were defeated. As the Roman Empire fell apart, the new groups of people scattered across the land. They were uneducated people who spoke different languages, and they replaced the more civilized Romans.