<human>:  Why did the population of the Roman Empire fall?
<bot>: The population of the Roman Empire fell because of a combination of wars, disease, and famine. The Romans had a huge empire, and they were very good at expanding it, but they weren't so good at defending it. The Roman army was very well equipped, but they didn't have enough money to pay for it. So they had to borrow money from other countries to keep up with their expenses.