Honorius in 395. Whilst divisions of the Roman Empire had occurred before, the Empire would never again be fully reunited. The reign of the sons of Theodosius I contributed heavily to the crisis that under the fifth century eventually resulted in the complete collapse of the western Roman court
.
The Eastern Empire was largely spared the difficulties faced by the West in the third and fourth centuries, due in part to a more firmly established urban culture and greater financial resources, which allowed it to placate invaders with tribute and pay foreign mercenaries. Throughout the fifth century, various invading armies overran the Western Empire but spared the east.
With the death of Theodosius in 395, the Roman Empire was divided once more between his two sons.
Honorius inherited the West. The Empire would never be reunited again, though Eastern Roman emperors, beginning with Zeno, would claim the de jure united title after Julius Nepos
Arcadius was a weak ruler, dominated by a series of figures behind the throne as he was more concerned with appearing to be a pious Christian than he was with political and military matters. The first such figure, Rufinus, engendered intense competition with the counterpart of Western Emperor Honorius, magister militum of half-Vandal origin Flavius Stilicho, who might have had him assassinated in 395 AD. Later figures in actual power would include consul Eutropius risen from eunuch, general Gainas of Gothic origin, his wife Aelia Eudoxia, the Patriarch John Chrysostom and Praetorian PrefectAnthemius.
war against the Sassanid Empire in the early 420s, on the pretext of persecuting Christians. He was forced to allow a stalemate however, as the Huns
were marching on Constantinople. The wars with the Huns were usually composed by Hunnic raids being followed by significant payments by the Eastern Empire so that the Huns would remain at peace with the Romans.
The death of Honorius of the West in 423 led Theodosius to supporting and eventually installing Valentinian III as Western Emperor in 425. To strengthen ties between East and West, Licinia Eudoxia, daughter of Theodosius, was betrothed to Valentinian.
Theodosius died in 450 as the result of a riding accident and was succeeded by Marcian, husband of his sister Pulcheria, as Eastern Emperor.
Marcian would reverse many of the actions taken by Theodosius II, particularly in terms of treaties with the Huns and in religious affairs. All Eastern Roman tributary payments to Attila ceased under Marcian while Attila was busy invading Italy. Marcian launched preemptive expeditions across the Danube into the Hunnic heartland, winning significant victories against them. The actions of Marcian, combined with famine in Italy, forced Attila to retreat back to the Hungarian plains where he would die in 453. After the death of Attila, Marcian would settle many formerly hunnic vassal tribes within Eastern Roman lands as foederati, taking advantage of the fall of the Hunnic empire.