The most straightforward theory for Western Rome’s collapse pins the fall on a string of military losses sustained against outside forces. In 476, the Germanic leader Odoacer staged a revolt and deposed the Emperor Romulus Augustulus. From then on, no Roman emperor would ever again rule from a post in Italy, leading many to cite 476 as the year the Western Empire suffered its deathblow.

Odovacer was a soldier and statesman of barbarian background, who deposed the child emperor Romulus Augustulus and became King of Italy (476–493). Odoacer's deposition of Romulus Augustulus is traditionally seen as marking the end of the Western Roman Empire as well as Ancient Rome.

Though the real power in Italy was in his hands, he represented himself as the client of the emperor in Constantinople, Zeno. Odoacer generally used the Roman honorific patrician, granted by Zeno, but was referred to as a king in many documents.

Odovacer himself used it in the only surviving official document that emanated from his chancery, and it was also used by the consul Basilius. Odoacer introduced few important changes into the administrative system of Italy. He had the support of the Roman Senate and was able to distribute land to his followers without much opposition. Unrest among his warriors led to violence in 477–478, but no such disturbances occurred during the later period of his reign. Although Odoacer was an Arian Christian, he rarely intervened in the affairs of the Trinitarian state church of the Roman Empire.

Odoacer was a military leader in Italy who led the revolt of Herulian, Rugian, and Scirian soldiers that deposed Romulus Augustulus on 4 September AD 476. Augustulus had been declared Western Roman Emperor by his father, the rebellious general of the army in Italy, less than a year before, but had been unable to gain allegiance or recognition beyond central Italy. With the backing of the Roman Senate, Odoacer thenceforth ruled Italy autonomously, paying lip service to the authority of Julius Nepos, the previous Western emperor, and Zeno, the emperor of the East.

Upon Nepos's murder in 480 Odoacer invaded Dalmatia, to punish the murderers. He did so, executing the conspirators, but within two years also conquered the region and incorporated it into his domain.

When Illus, master of soldiers of the Eastern Empire, asked for Odoacer's help in 484 in his struggle to depose Zeno, Odoacer invaded Zeno's westernmost provinces. The emperor responded first by inciting the Rugii of present-day Austria to attack Italy.

During the winter of 487–488 Odoacer crossed the Danube and defeated the Rugii in their own territory. Zeno also appointed the Ostrogoth Theodoric the Great who was menacing the borders of the Eastern Empire, to be king of Italy, turning one troublesome, nominal vassal against another.

Theodoric invaded Italy in 489 and by August 490 had captured almost the entire peninsula, forcing Odoacer to take refuge in Ravenna. The city surrendered on 5 March 493; Theodoric invited Odoacer to a banquet of reconciliation. Instead of forging an alliance, Theodoric killed the unsuspecting king.