I have come up with a solution to the problem of illegal immigrants from Mexico into the United States of America. The obvious problem is that it is caused by domestic issues of Mexico, yet it has a major effect on the US. As it is not a domestic issue of the US, the US cannot directly intervene. So we need to make the domestic issues of Mexico domestic issues of the United States. Annex Mexico.

I suspect that the initial costs towards influencing the political elite of Mexico to agree would cost ~$10b. USD in bribes. The cost of political absorption, infrastructure improvements, and converting the existing economy of Mexico to comply with US law could cost ~$500b. USD (cf. Unification of Germany). The recent escapade in Iraq shows that the US economy can endure such a cost without any major immediate problems.

Benefits:
-End of contentious and time-wasting debate on illegal immigration
-US population increased by 1/3, many new consumers for American businesses, new recruits for the struggling US military, etc.
-Guatemala border relatively trivial to defend
-Large oil reserves become US possessions

Drawbacks:
-Initially a major money-sink.
-A lot of legacy stuff has to be translated into Spanish