I had originally planned this post to be about integrating low level characters into Stage 3 exploration, acting as movers and shakers in campaign society and politics, but in the course of developing my thoughts, it's turned into something that I think is more broadly applicable to Stage 3 in general.
One of the concerns that's been raised about the Third Stage of exploration (i.e. the social and political landscape of the campaign world) is that it's too difficult for 1st level characters, that they need a bump in power or even to start above 1st level to succeed. I think that's nonsense. Ruling a barony certainly isn't the province of rookies and amateurs, but then, neither is slaying dragons. There are tiers of power in the political and social realm suitable for inexperienced characters, and in fact traditional character levels are of little relevance to a campaign of pure politics. Of course, combining traditional dungeon and wilderness adventuring with the conquest of the political arena allows far greater potential for heroic adventure. This is still D&D after all, not Mr. Smith Goes to Washington. For that reason, it's likely that a character's advancement in political power will run parallel to advancement in an adventuring class.
There is, in fact, a pretty sound reason why D&D characters start in the dungeon and aspire to politics. The fame and notoriety gained in personal adventures can translate directly to influence. A fighter who does nothing but roam the countryside performing heroic deeds until 9th level generally won't have much trouble impressing someone enough to give him a land grant and a title, or persuading the hero-worshiping populace of a town to elect him mayor. The reverse is seldom or never true - being a highly influential person doesn't in itself qualify one to slay dragons. It's possible to jump from the upper echelons of dungeoneering to the middle or upper echelons of politics with no prior experience, but making the analogous jump from the upper echelons of politics to the 10th level of the dungeon is strong evidence of a death wish. This is, obviously, a post hoc analysis of a game that in all likelihood was not designed with that fact in mind, but I think it's valid nonetheless. That said, none of this in any way precludes letting 1st level characters in a campaign of mixed Stages of Exploration jump right into politics, or indeed running a purely Stage 3 campaign in which the characters gain fantastic power in the political realm while never advancing beyond the beginning levels of an adventuring class. (I realize I'm almost making a case for separate tracking of character class XP and social/political influence, rather than awarding class XP for ruling a dominion, as the Companion Rules prescribe. I might have to explore this idea further...)
Before I get too far into this post, I want to make sure my terminology is clear. By political power I mean power to direct other people to do things, usually in the context of some sort of hierarchy or organization. This does include the compulsory sort of power wielded by governments, but there are purely voluntary forms as well, such as that of the head of a great merchant house, or Robin Hood leading his Merry Men. Wielding political power is akin to moving chessmen on the board.
In contrast, the typical adventurer gets things done with personal power - he fights his own battles, as it were. Wielding personal power, the character is his own piece on the board. Most of the time, the only political power PCs are likely to have from the beginning is the employer/henchman relationship, and that barely counts since the PC is usually right there in the thick of things alongside the henchman rather than sending him off on his own to carry out orders.
There are two sides to the coin of politically-oriented adventures: Gaining political power, and exercising it. In the case of adventurers, gaining political power is often accomplished, or at least facilitated, by the use of personal power. Characters perform services and quests and daring acts of heroism in order to gain influence, whether that be with the established seats of power in order to earn rank, or with the people at large as folk heroes. In many, if not most campaigns, that's the extent of it. Titles of nobility and other positions of prestige and honor are sought as intangible rewards, of no use in and of themselves in game terms. If the gaining of political power is to be used only as an end-game or as "campaign dressing" rather than actually affecting the course of play, then this is really nothing more than a Stage 1-2 game with the trappings, but not the substance, of Stage 3. Not that there's anything wrong with that.
In order to truly be Stage 3, at least as I understand it, characters must actually be able to wield their political power. They have to be able to lead their troops into battle, to negotiate treaties and agreements, to influence the flow of commerce, to direct the actions of their subjects, followers, and underlings. In wielding that power, they must be able to exert an observable and measurable influence on the campaign world. As I noted in my previous post, I think this requires, at the very least, systems for objectively quantifying power and influence, for resolving mass combat, and for finance and economics of governments and organizations.
Player characters might start out with no political power at all, and have to spend some time earning reputations and currying favor. On the other hand, there's plenty of precedent for low level characters wielding some political power, at least in the case of NPCs. Many a 1st or 2nd level character has been featured in modules and supplements as a mayor or council member of a village, a sergeant of the guard, or a thieves' guild officer. If the players are inclined toward political adventuring, it's no stretch at all to imagine that their characters might start out in such positions, especially if their starting age is over the stereotypical teens to early twenties.
Characters might begin as little fish in a big pond, holding or quickly seeking positions in the service of established powers like the crown, the nobility, or a major guild or church. They could also start with more direct influence, but less opportunity for advancement, with positions of authority in villages and backwater towns. Another possibility is to found their own guilds, secret societies, cults, insurrectionist movements, or what-have-you, the lowest possible starting point on the ladder of political power, but also the one with the greatest autonomy. As a footnote, PCs don't have to wield official power themselves; they can be quite powerful simply by having the ear of those who do.
Further reading: The illustrious swashbuckler Black Vulmea over at Really Bad Eggs has done a ton of research, thinking, and writing on campaign politics in his end game series. While it's geared more toward the cape-and-sword genre, there are a lot of great thoughts and ideas that can be adapted to a D&D campaign.