The decline of the Roman Empire was primarily caused by a combination of internal strife and external pressures. Internally, political instability, corruption, economic troubles, and social decay weakened the governance and infrastructure of the empire. Externally, barbarian invasions and migrations put immense strain on Roman borders. The division of the empire into Eastern and Western realms also contributed, with the Western Roman Empire falling in 476 AD. This multifaceted decline was gradual, leading to significant transformations in European society and the eventual rise of feudalism during the Middle Ages.