After the death of Emperor Marcus Aurelius in 180 AD, the Roman Empire slowly started to decline. Potential new emperors began to focus on pleasing the Senate at the expense of the general populace. The resulting political instability and corruption was just one reason for the fall of the empire.
This period marked the beginning of the Crisis of the Third Century, which involved civil wars, economic troubles, and external threats, contributing to the eventual disintegration of the Western Roman Empire.