Concerning the second problem, immigration, in #4.3 I argue that an important role of government, however arbitrary a society’s boundaries may appear from a historical point of view, is to be the effective agent of a people as they take responsibility for their territory and the size of their population, as well as for maintaining the land’s environmental integrity. Unless a definite agent is given responsibility for maintaining an asset and bears the responsibility and loss for not doing so, that asset tends to deteriorate. On my account the role of the institution of property is to prevent this deterioration from occurring. In the present case, the asset is the people’s territory and its potential capacity to support them in perpetuity; and the agent is the people itself as politically organized. The perpetuity condition is crucial. People must recognize that they cannot make up for failing to regulate their numbers or to care for their land by conquest in war, or by migrating into another people’s territory without their consent.
More briefly, Rawls opposed invade the world / invite the world.
Rawls went on to say countries that extrude numerous immigrants are at fault for being poorly run. For example, population pressure is partly the fault of a lack of women's rights. If immigrant-extruding countries managed their affairs on Rawlsian lines, then not so many of their people would try to leave. It's basically the same argument Jorge G. Castaneda made about Mexico in the 1990s.