From its creation as a separate empire following the death of Emperor Theodosius the Great in 395, the Western Roman Empire grew steadily weaker. Its territorial possessions in Europe were progressively dismembered by the barbarian tribes that surrounded them. Britain, Spain, France and Germany all fell away to poaching Angles, Goths, Vandals, Franks and Huns. Ultimately, little more than the Italian peninsula remained--and that itself was endangered. The imperial army became less reliable and effective as it began to rely increasingly on Goths and other barbarian mercenaries recruited to fill its ranks.

In 410 a daring Goth force seized and sacked the city of Rome itself, although the attackers quickly retreated. The city fell again in 455, this time to Vandal raiders from North Africa and Sicily, who held the city for two weeks before retiring. Finally, all semblance of effective leadership crumbled as succession to the imperial throne became mired in political maneuvering.

Out of the turmoil sprang an uprising among the barbarian mercenaries in the imperial army. Odoacer emerged as leader of the rebel movement, and in 476 he became the first barbarian ruler in Italy, with substantially all of the Italian mainland under his command. The Western Roman Empire was dead.

However, Odoacer was soon to find that too much success can be dangerous. He immediately set about consolidating and expanding his territory. In 476 he acquired the island of Sicily through treaty with the Vandals of North Africa. In subsequent campaigns Odoacer advanced first into Dalmatia in 481, then into the homeland of the Rugians to the north in 487. These expansionist trends soon provoked the concern of the Byzantine [Eastern Roman] Empire, as well as the ambition of Theodoric, whose Ostrogoth kingdom lay northeast of Italy.