IMO, Sustainability = carrying capacity of between 75 & 80%. Tops.
I dunno...
Africa? I is a huge drain, however, if those idiots could ever figure out how to get along, land issues, and democracy they would be net exporters and their third world conditions that Obama wants us to prop up would disappear.
How many Zimbabwes do they have?
Most of the third world conditions are dominated by islam, so perhaps the best bet is get rid of Islam in the UN.