Byzantium’s survival was undone by political and bureaucratic misrule. Perhaps the worst mistake was that of Justinian in sending Belisarius to defeat the barbarians and try to hold Rome — a gross waste of a military genius. Trade, diplomacy, and cultural diffusion would have worked in the long term to civilize the barbarian kingdoms and likely make them reliable allies against Islam.
I need to study up on this. It’s a huge Terra Incognita in my mind.
Justinian undermined the finances of everyone under his rule via massive taxation to bankroll his dream of reuniting the Roman Empire. By contrast, Basil II "the Bulgar-slayer" evolved into a great military leader in his own right, but left no children. The city managed to maintain itself despite its changing fortunes in the provinces, through oceangoing and even overland trade, even after Mad Mo the pedophile and his bloodthirsty cutthroat followers swept across N Africa and overthrew the Parthians.