Military leaders usurped power, rulers died of unnatural causes, revolts, plagues, fires, Christian persecutions.
285 - 305 CE
Diocletian splits the Roman Empire in 2, and adds junior emperors, so there are 4 caesars. When Diocletian and Maximian abdicate, there is civil war.
306 - 337 CE
In 312, Constantine defeats his co-emperor at the Milvian Bridge, and becomes sole ruler in the West. Later Constantine defeats the Eastern ruler and becomes sole ruler of the Roman Empire. Constantine establishes Christianity and creates a capital for the Roman Empire in the East, in Constantinople.
Fall of Official Paganism
360 - 363
Julian the Apostate attempts to reverse the religious trend to Christianity. He fails and dies in the East fighting the Parthians.
Battle of Adrianople
August 9, 378
Eastern Roman Emperor Valens is defeated by the Visigoths.
379 - 395
Theodosius reunites the Empire, but it doesn't last beyond his reign. At his death, the empire is divided by his sons, Arcadius, in the East, and Honorius, in the West.
Sack of Rome
401 - 410
Visigoths make incursions into Italy and in the end, under Alaric, sack Rome. This is one date given for the Fall of Rome.
Vandals Sack North Africa
429 - 435
Vandals, under Gaiseric, attack northern Africa, cutting off Roman grain supply.
440 - 454
Huns threaten Rome, are paid off, and then attack, making Rome and the army weak.
Vandals Sack Rome
Vandals plunder Rome but, by agreement, injure few people or buildings.
Fall of the Emperor of Rome
Last western emperor, Romulus Augustulus, is deposed by the barbarian general Odoacer who then rules Italy.