Take the regions of international conflict, and declare them human areas belonging to no country.
The idea is — declaring areas of conflict — "Human Areas" — as free and owned by no country, and protected by international special forces, obliged to preserve freedoms to internationally transparent, constructive and friendly activities.
This way, "Humanity" as entity could take away areas from countries, if they are conflicting, and at the locations of conflict, turning conflicts into opportunities, creating an incentive for countries to avoid conflict.
Then, all places owned by "Humanity" would have a special visa-free regulation, so anyone could go to live, work and have fun, without limitations of stay or requirement to leave.
To start off, some of the developed countries could donate some of their land areas at the borders (imagine, Finland and Sweden to open a "Human Area 1" fattening their border at some limited span) to help create exemplary "Human Areas" (prosperous economic zones). Then, motivation to serve the improvement livelihoods of people of the world in general, could be a cause noble enough to have the forces originally loyal to the particular countries to start working for creation of the new "Human Areas" as prosperous economic zones much desired. Given the security created in such zones, factories and service providers eventually may want to relocate, and the lands of "Humania" could become synonymous with prosperity :)
NOTE: I'm writing this, since cannot find the idea I've written before. In the previous description of the idea, that I can't find, there was numbering suggested, like: "Human Area 1", "Human Area 2", ..., "Human Area 51", and someone suggested that European Union works like that, though it doesn't, and someone suggested that an idea of "Refugeea" had been existing somewhere, except that refugees are usually powerless to claim land in ways that strong international communities believing in ensuring human (rather than nation) rights could.
Credits: Mindey of HalfBakery.