The Visigoths, following their sack of Rome in 410, eventually coexist peacefully with the Romans, farming and trading agricultural products and enslaved people for luxury goods.

They adopt many elements of Roman culture, some becoming literate in Latin.

The Western Roman Empire wields negligible military, political, or financial power by the time that the barbarian general Odoacer deposes the Emperor Romulus in 476, and has no effective control over the scattered Western domains that still describe themselves as Roman.

The Western Empire's legitimacy will last for centuries and its cultural influence remains today, but it will never have the strength to rise again.

The Hasdingi, the larger of the two branches of Vandals, had already been Christianized during the first half of the fourth century.

During the reign of Emperor Valens (364–78) the Vandals had accepted, much like the Goths earlier, Arianism, a belief that was in opposition to that of Nicene orthodoxy of the Roman Empire.

Yet there are also some scattered orthodox Vandals, among whom is the famous magister militum Stilicho, the chief minister of the Emperor Honorius.

Theodosius restores Valentinian II, still a very young man, as Augustus in the West.

He also appoints Arbogast, a pagan general of barbarian origin, as Valentinian's commander-in-chief and guardian.

Valentinian quarrels in public with Arbogast, fails to assert any authority, and dies at the age of twenty-one, either by suicide or by murder.

Arbogast and Theodosius fail to come to terms and Arbogast nominates an imperial official, Eugenius, as emperor in the West.

Eugenius makes some modest attempts to win pagan support, and with Arbogast leads a large army to fight another destructive civil war.

They are defeated and killed at the Battle of the Frigidus, which is attended by further heavy losses, especially among the Gothic federates of Theodosius.

The northeastern approaches to Italy will never be effectively garrisoned again.

Arbogast conducts a successful campaign in the winter of 393-394 against the Ripuarian Franks, the Chamavi (a Germanic tribe associated with the Franks), and along the Rhine.

Theodosius marches west in May 394 to suppress the revolution.

As in 388, he will make his way toward the Danube and then the Sava with his powerful army.

His force consists largely of barbarians and their allies, one of whose leaders is the German-born Roman general Flavius Stilicho, who in 385 had been appointed count of the domestics (commanding the Emperor's household troops) and in or before 393 had been named master of both services (i.e., commander in chief of the army).

Following Stilicho’s service on an embassy to the Persian king Shapur III, Theodosius had in 384 arranged the marriage of his favorite niece Serena, whom he had adopted as his daughter, to Stilicho, then an upcoming military officer, ensuring his loyalty to the House of Theodosius in the years ahead.

Stilicho has become the enemy of Rufinus, a native of Gaul who had risen to the rank of praetorian prefect of Illyricum, because of a difference of opinion about the treatment of some barbarian invaders in 389.

Theodosius' sons Arcadius and Honorius stay behind in the capital.

Arcadius, who had been given the right to promulgate laws independently, is supposed to direct the government in the East.

Theodosius first meets the forces of the usurper Eugenius, commanded by Arbogast, at the Frigidus River (modern Vipava River) on the eastern border of Italy, between Aquileia and Emona.

Theodosius' advance guard, composed almost entirely of Visigoth federates under Alaric on September 5, 394, suffers heavy losses during an attempted breakthrough and is only saved by nightfall.

The emperor ventures to attack the following day, however, and is victorious, due chiefly to the brilliant tactics of Stilicho.

The Battle of the Frigidus is part of a trend towards using increasing percentages of barbarian troops, especially in the west, where it will led to the weakening of the empire itself.

Eugenius had represented the last opportunity for the Pagans and the senatorial class to oppose the Christianization of the Empire.

Arbogast commits suicide immediately after the defeat, as does Nicomachus Flavianus, while Eugenius is held for execution as a criminal, his head afterward being displayed in Theodosius' camp.

Theodosius following the deaths of these three shows himself lenient and strives to achieve the settlement between opposing forces that is necessary to strengthen imperial unity.

He promotes Stilicho to generalissimo.

Theodosius had fallen ill, probably because of the exertion of the campaign, and goes to Milan, where he summons Honorius in order to present him formally as Augustus of the West, while intending to return his eldest son, Arcadius, to the East.