The study of Roman imperial history—which in practical terms began from the 60s BCE—presents the modern reader with certain paradigmatic issues relevant to governments and societies today. In broadest terms, the persistent dilemma was how to modify government structures and ethos as state and society expanded geographically and demographically. The republican ideal of Rome had somewhat made sense in a time when the state was little more than the preeminent city in a Mediterranean peninsular area, and needed to ensure its own survival and domination of surrounding locales. By the middle of the final century BCE, however, Rome had become the center of a multi-continent empire stretching from Spain to Iraq. Thus, one can present the continuing civil unrest from 80 to 30 BCE as the inability of an expanded city government to cope with the needs of an empire's administration.
Part of these needs consisted of large armies far from home. In such cases, powerful generals could emerge, and after Marius' military reforms of the 90s BCE, the soldiers in these legions became dependent upon generals for material survival. In turn, soldiers and veterans strengthened military leaders' political power as a pay-off. As the ensuing half-century showed, the Senate could not thwart a powerful general with charisma and a mass base of political support. Also lacking in a city government weighted down with imperial responsibilities was an efficient Empire-wide civil service and economic administration. Roman fiscal exactions and provincial administration often were, or at least appeared, erratic or irrational. A common pattern of Roman governance involved Rome responding ineffectually at first to a local disturbance, which grew to such extents that Rome had to invest large human and material assets to bring a resolution to a crisis that better administration would have prevented. Of course, Roman statesmen had long thought about reforms in their state and its relations to surrounding areas—Tiberius Gracchus had innovated new agrarian laws and moved toward increased political enfranchisement; Marius had reformed the army after disasters around 100 BCE; Sulla achieved undisputed power as Dictator and used it to reform the senatorial and equestrian orders; while Caesar, again as a Dictator—now perpetual—enacted reforms in the court system and in the administration of the provinces, as well as in the settlement of military veterans and in the increased granting of Roman and Latin citizenship to regions near the capital. Still and all, though, the inauguration of the Principate under Octavian Augustus was a totally new departure, and while his predecessors considered themselves to be reforming for the sake of the republic's survival, Augustus' new dispensation set the state on an entirely new course of political relations and dynamics. Indeed, though Augustus himself may not have even conceived it as such, the republic was superseded by his successors in favor of outright Empire with an authoritarian, if not autocratic, ruler.
This exposes another paradigmatic dilemma of the Roman Empire still relevant today. The excesses of Tiberius were irksome to the senatorial aristocracy, and there was some conspiracies against him. Still, imperial administration was passably good under him. The insanity of Caligula and later Nero, however, brought the state to the brink of civil war and anarchy. This meant that a persistent problem of the imperial period was in the growing personal rule of the sovereign. Too much relied on the wisdom and fitness of the ruler. Part of this was due to the close Emperor-military relationship. The military was always growing, and it depended entirely upon the Emperor. Conversely, an Emperor without military support was in peril. So, the personality of rule was continually problematic, and only at the end of the first century, when a truly professional civil service emerged, was the person of the Emperor somewhat less important. Still, checks and balances—a clear intent of republican period arrangements—were lacking, to the state and society's detriment.
In terms of the society, social enfranchisement, and elite circulation, the imperial era from 40 BCE to 161 CE was a dynamic period. While Rome-based patrician families dominated Roman society at the beginning through control of the Senate and urban wealth, from the 40s BCE, starting with measures under Caesar and picking up speed in the 40s and 80s CE, bourgeoisie and wealthier elements from the regions of Italy and certain provinces such as southern Gaul and Iberia began to enter the elite arena. Many of them were of equestrian origin: knights-turned-businessmen with financial interests in the capital. By the early part of the first century, growing numbers of this new class were being enrolled in the Senate on the Princeps' initiative. By the time of Vespasianus (70 CE), emperors could emerge from that class. Thus, an enfranchisement of people beyond Rome's gates was well under way.
Another part of the evolution in Rome, especially beginning in Claudius' time (40s CE), involved the tribal elements from Gaul and other eastern areas. Sometimes with imperial support, they were allowed to run for positions of middling elite power, and over generations, they too—be it from Gaul, along the Rhine, or the Greek parts—could ascend to senatorial rank. Of course, certain emperor's use of freedmen in administration also aided this process.
Also in ethnic terms, the end of the era described in this SparkNote, under Marcus Aurelias in particular, brings Rome face to face with what would become its most enduring, insurmountable challenge: the German Barbarians. From the time of Augustus, Rome had seen the German tribes as a military threat, source of labor, and a reservoir of auxiliary military forces. Some elements of Germanic society were, by the end of the second century, entering the Roman world, learning Latin, and becoming partially Romanized. Of course, areas near the Danube, conquered in phases throughout the period, became thoroughly Romanized by the third century, providing the majority of the Empire's generals, and several emperors.
In the midst of all these political, military, and social issues of relevance to our era was the economic situation. Rome was one of the ancient worlds' wealthiest cities, with the largest population. Its government could count on the material basis to undertake almost any initiative. This strength, however, was in some respects illusory. Based on tribute from provinces as well as booty from war, the Roman economy was still ancient, primitive, and strikingly unproductive, non-innovative, and underdeveloped for the resources at the state elite's disposal. The continuing, unresolved question was how to achieve sustainable development, as opposed to mere extractive growth and exploitation of the imperial margins. Rome never came to a satisfactory answer, and this failure would have tremendous consequences in the period just after the 160s CE, when the Roman glue would begin to weaken.
Thus, in almost every aspect, Roman history from 50 BCE to 161 CE illustrates those challenges characteristic of governance and societal order in all the relatively advanced states that followed it, in the early modern and modern centuries in particular. Hence its enduring popularity and didactic value, and hence those qualities that so dramatically set it off from the medieval morass that was to follow it.