Huge Interstellar Empires And Why They Don't Last

Huge, interstellar, possibly galactic or even intergalactic empires are a usual sight in science fiction. Either they serve as an adversary to the freedom-fighting species around the galaxy, vicious militant aliens threatening earth or, in some cases, efficient and relatively benign and human-ruled.
In my previous entry I threaded upon the subject of FTL and interstellar society. Let us continue on that and assume that there exists, in the known space of this FTL travel society, an empire. This empire spans most of the known space. We shall assume that in this case, empire also means an autocratic monarchy. Let us call the supreme ruler emperor, although other titles might be as good. Even president, supreme chancellor or other superficially democratic titles. The fact remains that the emperor has control.

How does he have control? Either it is through religion, by controlling the clergy of the state religion (mandatory for all) and through the clergy promotes the emperor as divine or having a divine mandate to rule. It might be that his armed forces are superior to any other and he rules through threat of armes. He might distribute power to powerful warlords and form a sort of nobility (bureaucratic or martial) and have them rule far-off territories. This might cause the nobility to have more actual power (at least combined) than the emperor. And thus the Imperial Court would be a stage for intrigue, backstabbing and dark deals. And the emperor's spies would be everywhere. A theocratic empire keeps control through indoctrination. A theocratic empire does not happen overnight, though. It might be that the emperor is a figure drawn from a former religious leader slowly becoming a political and military leader. Or it might be that the emperor embraces a religion and the religion will be protective of it's most powerful patron. It also might be in this case that the religious leaders become very political. A theocratic feudal empire might even divide it's territories by diocese and set bishops and cardinals (or sheiks or whatever) to rule the territories directly.

How the system is created is equally important. Has the empire been created by conquest and assimilation or has it been a natural evolution of political power, ending in a stable (or somewhat stable) monarchy?

The creation by conquest has two major points. One is that the martial nobility is practically created by default. Military governors are appointed to conquered worlds even though they might be allowed to have some degree of autonomy and keep their local laws. There would be a garrison of imperial troops and possibly some ships in orbit, at least for a while. Military governors might eventually obtain a permanent and possibly hereditary claim to the world they administered or, to prevent such claims, the governors are cycled and replaced on a regular basis. In this case, powerful military leaders would gain much say in the Imperial court. This might be preferable to hereditary governors, since a military leaders might more often rise through the ranks by merit and skill rather than family influence. The second point is that the conquered territories are likely to harbor resentment towards the imperial authority and there would be a rebellion at any given moment on some world. Through assimilation, forced relocations and other harsh methods peace might be eventually obtained, but continued military presence on occupied worlds would cause a long-term strain on the imperial armed forces.

Natural evolution happens when a stellar state, probably under some sort of transition and crisis, hands over much power to a capable individual. This individual clears the crisis and as he does the job so well, more power is given to him. Alternatively, jealous powers might challenge him and force a civil war or political crisis. The leader would now have a good reason to gain absolute or almost absolute power "for the duration of the crisis". In the case of the Roman Republic, Caesar was assassinated quite shortly after winning the civil war, prompting another round of civil wars before Augustus, his legal heir, could assert his own authority. The civil war or other crisis to gain emergency powers could be faked or it could be manufactured and manipulated into happening, of course. But fact remains that evolution from a parliamentary (or other kind of plural rule) to autocratic is mostly triggered by a severe crisis, even though there might have been a slower move towards favouring strongman rule, possibly be long-term problems or recurring problems that need a swift hand.

Now, space. As with terrestial empires, geography (or should it be astrography in case of space?) and technology limits the boundaries of the empire. If distances between capital and outermost territories are long and the journey difficult, it will be a constant and expensive problem to keep the border territories. The border territories might even be partly or completely independent, serving as buffer states.

History has taught that if empires grow too large, they start to have management problems, bureaucratic expenses skyrocket and the society as a whole stagnates. And a stagnant society may be overrun by a less stagnant competitor or the empire might collapse under economic strain to several lesser states, ruled by the former governor or powerful warlords. Or (most probably) a collection of reasons, including the two mentioned.