Question

Why did Justinian I fail to regain all of the former provinces of the old Roman Empire?

Answer 1

There were a number of factors involved, but the simplest explanation is that he simply reached for too much by overextending the resources of the Byzantine Empire and ultimately draining its coffers to near bankruptcy.

In the last years of Justinian's reign, a mighty army that once numbered more than half a million soldiers was whittled down to 150,000, hardly enough to man the frontier fortresses built to protect the newly expanded borders of a united empire against enemies that sensed weakness and sought to take swift advantage of it at every opportunity.

While a lot is made of his conquests, they didn't last as war continued over his conquered territories many of which were reclaimed after his death. He might have made the Mediterranean a Roman lake once again by the time he died in 565, but it was on shaky ground. His conquests in

The people that lived in the West weren't the kind of "barbarian" savages that existed during the reign of the Roman Empire - they had learned how to adopt the same fighting tactics and were led by a number of strong personalities such as Totila of the Ostrogoths who reclaimed Italy from the Byzantines during the Gothic Wars. Justinian then sent the eunuch, Narses, to take it back until it was lost again in the Lombard invasion that began in 568 AD - three years after Justinian's death.

Even the capital was threatened by a tribe of Huns called the Kotrigurs at one point in 559. His best general, Belisarius, could have destroyed them but ambushed them instead with a small force given that there were not that many soldiers he was given and Justinian bought them off with tribute as he often did with many enemies, further draining the imperial treasury.

Justinian also had his hands full in fending off the Persians in the East who were pressing against his borders. Payments of tribute had also drained the treasury along with Justinian's massive building programs and occupied the attention of the Byzantine military which left its armies in the West fighting with what seemed to be one hand tied behind their backs.

Answer 2

A good case can be made for the outbreak of the plague, which began in 541 AD and recurred in waves until almost 750, and succeeded in killing perhaps as much as 25% of the population of the Byzantine Empire, and as much as 40% of the population of its capital. The first and most virulent outbreak is called the Plague of Justinian, because he was emperor at the time. (He actually contracted it, but survived.)

The plague may have affected the city-dwelling Byzantines more than the more rural Germanic tribes they fought, because their more centralized and communicating societies spread the bacillus more rapidly. Also relevant is the fact that the Empire stopped being able to sustain the massive expenditures necessary for conquest, as population declined and tax revenues plummeted.