All the US needs to do is make "illegal" immigrants pay for things such as taxes, health insurance, hospital bills, various state fees, parking tickets, and whatnot. But there's no way to enforce this, and employers really really like to have illegal immigrants working for them. I do believe that Mexico will eventually become part of the US, but not anytime soon. There's really no easy solution to the immigrant issue, and EU nations supposedly have a very similar issue there, although they actually have decent welfare systems and they are obligated to take care of anyone who is part of the EU. The world is on its way to a unified global system, but it's going to take awhile, and it's going to be difficult.