Coming back to this to flesh things out a bit:
AD 370s
A large group of Goths migrate into the Roman Empire. The situation is delicate, but they are successfully pacified and given asylum in several locations across the empire.
AD 380s
Valentinian, Augustus of the West, dies in AD 380. His 21 year old son, Gratian, is proclaimed Caesar of the east, under his brother, Valens, while his younger son, Valentinian II, is proclaimed Augustus of the West at age 9, as a puppet under the Frankish general Merobaudes and a junta of other military officers. Valens, Augustus of the East, dies in 387, and succeeded by Gratian. Merobaudes has been supplanted by Stilicho, the new Magister Militum of the West. In the East, Theodosius the Younger is Magister Militum.
AD 400s
After constant, but relatively minor, raiding by the various Germanic tribes, a large scale invasion is initiated over the course of the winter, as a loose confederation of tribes under the leadership of a Vandal king, Gunderic. After a few brief skirmishes in which the loyalties of Stilicho, also of Vandal extraction, were cast into doubt, he was executed and replaced by Alaric, a Roman commander of Gothic ethnicity. A full year of battles are required to eventually defeat the Vandal confederation, most of the various allied tribes are settled in Roman territory, and the Vandals are forced back across the Rhine to serve as a buffer against the Huns. At the end of 407, Gratian dies, and the Eastern Empire comes to his son by Flavia Maxima Constantia, Constantius III.
AD 410s
Valentinian II dies, and is succeeded by his nephew, and son of Theodosius the Younger, Arcadius. Arcadius, like Valentinian II was in his youth, was a mere puppet of the Magister Militum, Alaric. The Western borders continue to face constant pressure, and most of Alaric's time is spent racing from the Rhine to the Danube and back again.
AD 420s
Alaric dies and, after a brief power struggle among the military, one Flavius Aetius becomes Magister Militum. His term in the office will be dominated by conflicts with the Huns, with whom he has nominally good relations. Constantius III dies and is succeeded by his brother, Constans II as Augustus of the East.
AD 430s
Civil war consumes the Western Empire after the death of Arcadius. Multiple claimants are elevated and the frontiers, already very porous, are threatened greatly as the Huns take advantage of the opportunity. Britannia is overrun by Saxon raiders, and the Franks expand their holdings in northern Gallia during the chaos.
AD 440s
Theodosius, son of Alaric and Galla Placidia, daughter of Theodosius the Younger and Galla (daughter of Valentinian), wins the support of Aetius and is proclaimed as Augustus. His ascension, though he's certainly of the Imperial family, marks the beginning of the so-called Gothic dynasty. Over the course of the decade, the remaining claimants are crushed and Theodosius reigns unopposed. Constans II dies and is succeeded by his nephew, Olybrius.
AD 450s
Theodosius and Aetius defeat a major Hunnic army, after which Aetius is exiled so as to consolidate Theodosius' hold on power. Theodosius then goes on to restore Roman authority in Britannia. By the end of the decade, the Vandals, Alemanni, Burgundians, and Suevi, are all either completely defeated or incorporated into the Empire. The Franks are still semi-independent in the north of Gallia, and a large contingent of the Goths are still independent in the Balkans, between the two halves of the Empire.
AD 460s
The Hunnic Empire collapses after a second defeat, this time by the Eastern Empire. Olybrius is killed in the battle, opening up a power vacuum and leading to intermittent civil war in the East over the coming years. Theodosius campaigns against the Franks in order to solidify Roman authority over them. Agreeable tribes are left in place, while the more intransigent Franks are dispersed through the Empire. Theodosius dies in 467, and is succeeded by his son, Romulus Maximus.
AD 470s
The Sassanid Persians take advantage of the instability of the Eastern Empire and invade. With the frontiers in the West relatively stable for the first time in living memory, Romulus Maximus marches an army to the assistance of his Eastern colleague, Anastasius. The combined armies of East and West defeat the Sassanids outside of Amida, and a status quo peace is secured. In 476, Anatasius dies, and Romulus Maximus succeeds him, ruling over a united Roman Empire.