A law of 90 BC (Lex Julia) offered Roman citizenship to the federate states that accepted the terms.
As loyalties wavered and became more local, the empire then began to devolve into smaller territories and closer personal fealties.
[1] The Franks became foederati in 358, when Emperor Julian let them keep the areas in northern Roman Gaul, which had been depopulated during the preceding century.
In 376, some of the Goths asked Emperor Valens to allow them to settle on the southern bank of the Danube River and were accepted into the empire as foederati.
Joannes, a high-ranking officer, lacked a strong army and fortified himself in his capital, Ravenna, where he was killed in the summer of 425.
Soon, Aetius returned to Italy with a large force of Huns to find that power in the west was now in the hands of Valentinian III and his mother, Galla Placidia.
By the 5th century, lacking the wealth needed to pay and train a professional army, the Western Roman Empire's military strength was almost entirely reliant on foederati units.
Even before the eventual fall of the Western Roman Empire in 476, several kingdoms with the status of foederati had managed to gain a full independence that was formally recognised by the Western Roman Empire, such as the Vandals in the peace treaty concluded in 442 between their king, Genseric, and Valentinian III[2] and the Visigoths through the peace treaty concluded in 475 between their king Euric and Julius Nepos.
[4] Foederati (transliterated in Greek as Φοιδερᾶτοι or translated as Σύμμαχοι) were still present in the East Roman army during the 6th century.
[5] These armies also included non-Roman elements such as Hunnic archers and Herule mercenaries who were more akin to traditional foederati but who were now referred to as symmachoi.