This RPGnet thread got me thinking about social intrigue and political maneuvering in RPG:s. Could one cook up a game only about manipulating others? Probably, but there are some popular tropes about politics that need to be handled.
The main one is "You owe me one!", which is the subject of the thread I linked above. A recurring theme in that thread is that existing games either make you pay back favors or present loss of "honor" if you don't. The key is to make favors a hard currency - it's as important as a character's hit points, gold or magical powers.
The easy way would be to track favors owed. Earning favors would be done by aiding others, but it would only count for favors owed if they asked for it, or if their lives were saved. Once someone owes you a favor, you can cash it in at any time in exchange for... a favor that that person can grant. If he refuses, he loses social standing - in the terms of this system, all favors owed to that person are voided, since everyone knows he is not trustworthy, and thus no-one is expected to honor deals made with him.
One would have to perform some form of atonement to get back into people's favor - in most pseudo-fantasy settings, this might require a substantial donation to the church, or doing a quest for them in case you're poor.
Example: Rethgif the PC rescued King Gnik's daughter in a recent adventure. The king now owes Rethgif a favor. (The other PC:s got paid and thus aren't owed.) Rethgif can ask the king for one (non-suicidal) favor that the king can reasonably grant and the king has to comply or be branded as an untrustworthy person, losing any favors that are owed to him (probably plenty). Kings don't particularly want to owe people favors - because they are owed lots of favors that they can lose - but sometimes have no choice.
Of course, player characters can owe favors too. Great way to pull them into adventures as long as they care about their carefully spun web of favors owed to them. (Emergent behavior: The more embroiled someone is in the politics of a nation, the more they have to lose from stepping outside the social norms of that nation.)
Finally, I want to reiterate something - the key to making this work is to let the players know that favors are a hard currency. Being owed a favor by the king is huge. And somehow, even favors owed by the thieves' guildmaster are known about by the relevant people, so he can't cheat this system.