Diocletian was able to bring Rome together to find peace and financial success, but he ended up destroying the unity of Rome by dividing power into what was known as the tetrarchy. Diocletian and Maximian shared the title of Augustus with two generals, Constantius and Galerius, who were appointed to succeed them and rule the empire. While they were able to maintain peace for a time, the empire fell apart when Diocletian retired.
Once Diocletian and Maximian retired, the struggle for power over the entire empire began. The winner was eventually Constantine, who became the sole emperor of Rome in 324 A.D. While emperor, Constantine changed many things about Rome. He first moved the capital city to Byzantium and then renamed it after himself, calling it Constantinople. He also made Christianity the official religion of Rome.
Thirty years after the death of Constantine, Rome was once again divided into east and west empires with continual warring between the two as well as with the Persian empire. This division and constant strife led to the final collapse of the Roman empire in 476 A.D.
Rome lasted almost 500 years as the most powerful empire in the world. Although Diocletian is often listed in the reasons for Rome's demise, historians also point to other factors, such as debilitating taxation, climate change, military losses and natural disasters.