With a POD after 1980, have droves of Europeans emigrating to the US. The European immigrants to the US must outnumber immigrants from any other continet by a large ammount. Your only real restriction is that you can't screw around with the climate or such stuff that is out of the control of man (so don't just have a massive famine in Europe).
Also, what are the effects of this?
Also, what are the effects of this?