Will: trying to have different cultures living under the one state-law (via imperialism and mass economic/capitalist immigration/emigration will always cause problems - the latest example, in our news, is China.
Whilst the ideal of having the land, the culture, and the law of the land all linked (with eco-tourism and fair-trade between different lands) may never be reached, making economic/capitalist immigration/emigration illegal, via the UN, from now on, will make our world a more peaceful and interesting place.