The Roman Empire was divided into Eastern and Western halves in the 4th century AD, primarily under the rule of Emperor Diocletian. This division aimed to improve administrative efficiency, as the Empire faced numerous internal and external challenges, including economic strife and military threats. The Eastern Roman Empire, later known as the Byzantine Empire, thrived for centuries, preserving much of Roman law and culture. In contrast, the Western Roman Empire struggled with increasing invasions and political instability, ultimately falling in 476 AD. This division significantly influenced the development of European history and culture.