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Why did Justinian I launch a war against the Ostrogoths in Italy?

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Mosaic detail of Emperor Justinian I with a jeweled crown and halo, wearing ornate robes, from the Church of San Vitale in Ravenna, Italy. — Justinian I Justinian I, detail of a mosaic in the Church of San Vitale, Ravenna, Italy.

Justinian I launched a war against the Ostrogoths in Italy primarily to reassert direct imperial control over the region, which he considered the mother province of the Roman Empire, and to support fellow Catholics living under the rule of Arian Germanic leaders.12

Following the death of the Ostrogothic king Theodoric in 526, political instability emerged in Italy. The situation provided Justinian with a strategic opportunity when the regent Amalasuntha, who had maintained cordial relations with Constantinople, was assassinated. Justinian used this event as a pretext to protest the murder and intervene.2

Justinian’s ambitions were further fueled by his desire to reclaim provinces lost to the empire through what he viewed as previous indolence. By 535, having already achieved success against the Vandals in North Africa, he dispatched an army and a fleet under Belisarius to attack Sicily, marking the beginning of a prolonged conflict to restore Roman authority in the Italian peninsula.12