Another thing that is often left out of the equation is: what was the birth rate in the country of destination when the mass migration started?
                  In the states the birth rate had leveled off and we were very proud of the fact that we were holding our own, and doing our part to protect the environment. After years of mass immigration, the native birth rate has began to pick up--maybe in self defence, I don't know--and the whole thing is rocketing off the charts.
                  It would be interesting to know what the birth rates were at the time(s) of the migrations cited above.