I have decided to adopt the term "Imperium," from the official Traveller setting, for use in my Terran Space setting. In this incarnation, it will be more specifically refereed to as the Terran Imperium, but will resemble its more official cousin in a number of ways. As Rob Conley notes in his post about the Imperium, there are numerous ways one can interpret it. In this post I will seek to find out what I can about the Imperium from the Mongoose Traveller core book and attempt to bring these aspects together into a cohesive whole.
The first thing one notices about Traveller's setting assumptions is that the setting possesses forms of nobility. One's social standing stat decides whether or not one is a member of the noble or working classes. The titles, which are ones one would normally associate with European forms of nobility, hint at a roughly feudal structure. It could be that this future state merely adopted them due to some form of cultural memory. For the time being, I will leave the question of feudalism up in the air.
Second, we see by that the Imperium has a standing military, due to the fact that a character can have served in it before mustering out. Such institutions are usually signs of highly nationalized groups. It is quite difficult to maintain a standing army without some sense of common identity. One would not expect to see a standing military in the feudal system hinted at above, but the two can be brought together as discussed below.
Now for two more subtle clues. We can see from the world generation system that worlds within the Imperium can have a number of different forms of government. A participating democracy is just as likely to have a Consulate present as a religious dictatorship. One can assume then that these polities enjoy a large degree of autonomy. It is worth noting that some of these worlds might be independent, since the subsector generation rules suggest that multiple states can exist within a single subsector. Still, I think it's fair to assume that the Imperium usually lets a system decide its own internal forms of government.
The other subtle clue comes, once again, from character creation. It appears that the Imperium was recently at war. Events for naval characters reveal that they could have participated in a major battle, and similar hints may be found in other careers. For my purposes, this war was with an external alien empire whose exact nature is still being determined. Such a threat would be enough to cause some fairly dramatic social change within the Imperium.
For the sake of argument, let us say that the Imperium was formerly a more or less feudal organization. Power filtered down from Terra, but due to the problems of ruling an interstellar state without FTL communication the Emperor (or perhaps the Senate) delegated administrative duties among a class of people loyal to him (it). These independent servants of the Imperium were more or less allowed to govern as they wished, assuming they provided monetary and military support when needed. Such a system would overcome some of the difficulties created by the large amounts of space between star systems, but would be too decentralized to respond to major threats to Imperial safety.
A major war with an alien civilization could have forced the Imperium's hand. The ineffectiveness of certain barons may have necessitated the creation of a standing military to better respond to the alien threat. While benefiting the general welfare of the citizens of the Imperium, this change would have come at the cost of some of the autonomy of the nobility and/or the various planets.
One might think of the Imperium as a society in the midst of change. Nobles still exist and exert an immense amount of control on the governmental system, even as the methods of organization and mustering that once made them a necessity are now becoming obsolete. The underclass is increasingly becoming important since the nobility no longer monopolizes the use of force. Also the stability created by a standing military and scout patrol increases the opportunities for interstellar trade, increasing the power of the mercantile class further.
I'm not entirely sold on this version yet, especially in light of the core rulebooks suggestion to let the results of sector generation define the polities of the setting. Still, I think this is a workable model and one I find extremely attractive.