The decline of Rome was due to a combination of factors, including political instability, economic troubles, and military defeats. Over time, the empire became too large to manage effectively, leading to administrative difficulties and corruption. Barbarian invasions, particularly the Visigoths' sack of Rome in 410 AD and the Vandals in 455 AD, were critical blows. Additionally, the split of the empire into Eastern and Western halves in 285 AD weakened Rome, making it more vulnerable to external threats.