What happened
Odoacer commanded the Germanic troops in Roman service, and the crisis began when Rome refused them land in Italy. He beat and killed the boy emperor’s father Orestes at Pavia, took Ravenna on 4 September, and then sent the imperial regalia to Constantinople, asking only to be recognised as a patrician governing Italy on the eastern emperor’s behalf. Nobody present thought an empire had ended: Julius Nepos, the emperor Orestes had driven out four years earlier, was still alive in Dalmatia and still recognised in the east until his murder in 480. The date became an ending later, when historians needed one.
Background
The West had long declined: division from the East (395), barbarian invasions and settlements, the sacks of Rome in 410 (Visigoths) and 455 (Vandals), shrinking revenue, and puppet emperors. Odoacer made himself king in Italy under nominal eastern authority.
Consequences
Roman political rule in the West ended, giving way to Germanic kingdoms, while the Eastern (Byzantine) Empire continued for another thousand years. Historians treat 476 as a symbolic marker rather than a sudden break, since Roman institutions and culture persisted.