The short answer: Sometimes.

Here’s one example. By 527 A.D., the Eastern Roman Empire at Constantinople seemed fated to collapse like the West had a near century prior. The Persian Sassanids were gobbling up Byzantine lands in the east. Almost all of old Rome west of Greece had already been lost.

A growing and unsustainable administrative state exercised near control of Constantinople. Christianity was splintering into irrelevant factionalism. The law was a selective mess.

Justinian was certainly an unlikely emperor: an outsider of peasant stock from the northern frontier, an Eastern Latin rather than Greek speaker (and likely the last native Latin-speaking emperor), who would marry an infamous but shrewd courtesan, Theodora.

Yet in some 38 years of sometimes brutal rule, Justinian through the leadership of his brilliant generals, Belisarius and Narses, stabilized the eastern borders. He reclaimed for eastern Rome North Africa, Sicily, much of Italy, and some of Spain, often through small, well-organized armies and prudent alliances. He reformed the bureaucracy, systematized Roman law (Codex Justinianus), and built the magnificent Christian cathedral of Hagia Sophia—the largest church in the world for a thousand years.

Justinian might have done even far more had not a devastating three-year epidemic of bubonic plague spiked and wiped out a quarter of the empire’s population. The millions of losses created a permanent manpower shortage that left the Byzantines vulnerable to relentless Gothic enemies in Western Europe—and ultimately, a century and a half later, the conquests of new Islamic armies in the Middle East and North Africa. ...