To get back to that snapshot of the Byzantine Empire and its relationship to oligarchs, now is the time to flesh out that picture a little more. Chiefly, we'll do this by describing in brief the political and economic culture of the empire at the time.
Yes, political and economic culture. I mentioned that the Byzantine Empire was highly centralized and preferred to keep a tight leash on its oligarchs, whereas the United States liked to let them run amok. This description of empires in individualistic terms does have some provisional functionality, as their "interests" roughly track with very general tendencies specific to their character.
But underneath those provisional designations are vastly complicated societies full of a multitude of individuals, all interacting with each other and with the outside, occupying complex gradients of power that are exercised when those individuals interact with each other in concert as factions or economic blocs for various purposes.
The character of these interactions could roughly be described as a given society's political and economic culture. As is the usual case with this sort of thing, we can turn to an example in which the Byzantine empire was in a period of transition, which illuminated the boundaries and tendencies of a culture that was undergoing strain under dramatic change.
When the Byzantine re-expansion really got going in the 900's - after an intensely lean period of contraction and hardship, and relations with its neighbors re-normalized, and the Arab expansions abated and were beaten back - the empire began to rely more heavily on oligarchs (or magnates) for military conquest and territorial reacquisitions. This budding relationship bore fruit when Nicephorus (of the prominent magnate family Phocas) was crowned emperor after the abrupt death of emperor Romanos II.
Due to his popular reputation as a military legend, who had beaten back Arab forces and taken back various territories lost over a century ago, Nicephorus seemed an obvious choice as emperor and was elevated by his army. Interestingly though, it only took a couple of years for the body politic to completely reverse this opinion, perceiving him as an outside intruder and ejecting him in a sense as a foreign body.
This was due in large part to the Byzantine political and economic culture at the time. A lot of the power behind the empire was situated in the civil services and the Constantinople-based aristocracy, who were well-accustomed to the concentration of power in the empire's court in that city, through the central tax system and the networks of distribution taking place there, and this was a system cultivated over hundreds of years within the city walls by necessity of a long period of fraught survival, engraving a distinct political and economic culture peculiar to the empire.
The sudden re-expansion of the empire's boundaries was, without qualification, a good thing materially for the empire, with its population enjoying a growing prosperity not seen in quite some time. However, at the same time, that re-expansion was experienced as a trauma as the forces driving it touched down within the empire's existing political and economic machinery, clashing with it.
Outside of the walls of Constantinople, Nicephorus and his army were worshipped as heroes for their brilliant conquests of surrounding regions, but once within the walls of the city and serving as emperor, the story changed dramatically. It didn't help that Nicephorus was clumsy as politician and ruler, unable to transfer his military brilliance to the role, but what ultimately did him in were the discontinuities he brought to the existing culture as harbinger of the changing economic and political climate.
Nicephorus' reforms were perceived as highly disruptive to the existing centralized court system, with his presence and his outside ties redirecting the reciprocal flow of wealth and favor distribution to the army and his magnate family and associates. At the same time, he was incurring heavy taxes on the populace in favor of resource-intensive military aims, redirecting resources to his army. He was also alienating the church by attempting to insert a warrior ethos into the prevailing Christian theology of the empire.
Ultimately, his reign suffered a coup which culminated in his assassination, a scheme that was advanced and succeeded based not only on factional support for this bold transgression within the regime, but also on the notion of his unpopularity as ruler and the perception of his foreign quality by the body politic. This was confirmed after one of the coup conspirators, Nicephorus' nephew John I Tzimiskes assumed the throne and was accepted as ruler.
Tzimiskes continued on the family's rule, this time as a better politician than Nicephorus was. Curious, you can see the shift in phase of the empire's political and economic system, eased through by an assassination and usurpation of the throne by another family member as the traumas of the shift settled, like timber cut and shaped to fit a joint.
To summarize and generalize this, a society's political and economic culture plays a large part in where power flows, in what way it is legitimated, and how it is exercised, which places real constraints on the shape that society takes and how it operates. This culture can change very slowly over time, or it can transform very rapidly through the course of violent trauma, catastrophe, and broad-based convulsions, but it often takes the latter set of extreme circumstances for those really big and dramatic changes.
Even the powerful and supposedly autocratic Roman emperors (the canny ones that could keep their power anyway) would pay careful attention to public opinion, such as when announcing and testing policies, engaging in public works, and putting on games, triumphs, and other spectacles. Because they knew that their rivals were also paying attention, watching for signs of mass displeasure, which was taken as weakness and an opportunity to strike.
This was one manifestation of what is commonly called the "writing on the wall," or the visible manifestation of those invisible relations and forces that can determine the fate of powerful people.
