Perhaps a return to Nation-states which ultimately run themselves based on a generalized global legal system with a global legal court. These nation-states are based around each local area with a set population greater than a certain number, bounded by a set area. These areas control that set amount of area in which they occupy, but the land itself not being owned by them. Each of these Nation-states would then be represented in a world democracy in which major world events are voted on in response to certain actions or major changes needing to be made, while still responsability for local politics falls on the nation-states themselves.

Land ownership would be done away with, as the land itself is a shared property of all mankind. So we create an enviormental court to determine usage of the land by global co-ops (Falling back on my corporate reworking from a previous post) for the use of that land. We only have one world and a limited amount of resources, they should all be used to benifit us all, not a select few.