My last post on Domain Play in Superhero RPGs received a fair amount of discussion which gave me some additional food for thought.
One of the biggest takeaways is there are two primary ways of handling a PC or major NPC ruling over a nation in a superhero game (or any other genre as well). The easiest way would be to simply make it a point of the character's background. In many comic books, the fact that a character rules or is royalty in a far-off land is perhaps an interesting plot point that gets used every once in a while. This is fairly common in comic books, particularly in the Silver and Bronze Ages.
If, on the other hand, domain play were to be a major point in the game, then you would want to have rules that facilitate such a game. You would want to manage the domain's resources, be able to generate events, handle conflicts/alliances/wars with other domains, managing espionage, etc. You'd certainly want this to be superhero-centric. For example, a dispute on the taxation of certain trade routes probably does not make for a compelling superhero adventure. On the other hand, events like nuclear tests damaging Atlantis or becoming known as a refuge for mutants make for potential superhero adventures. I'm picturing a system like the domain management found in ACKS or in Mongoose Publishing's RuneQuest Empires or Arc Dream's Grim War.
Finally, in keeping with the "Captain America for President" image I used in this post, it bears thinking that superheroes and supervillains have also gone on to rule real countries in superhero universes. For example, while Captain America of the main Marvel Universe never did run for president, the Ultimate universe's Captain America did become president. Similarly, Lex Luthor was, for several years, president. In Marvel's New Universe, Philip Nolan Voigt used his powers to become president. Given he had the ability to absorb other's powers, he made good use of mind control in his presidential campaign. On at least one parallel universe, Superman became president, something that would truly drive birthers bonkers...