There's been a lot of negative vibes on the boards recently, so let's just dream for a minute.
What kind of political system would a world living in peace and harmony need? Obviously we'd need to nuke the shit out of the world and start over, but that's OK as long as the result is for the greater good.
I would install a benevolent dictator in every country of the world, each with slightly different ideals so people could choose to live in a country that suits them. For people who like to break shit and generally ruin things, I would reserve the Americas, where there are no laws so if you go there you basically know what you're getting yourself into. North America would be desert Mad Max world and South America would be Indiana Jones jungle world. It'll be awesome.