Diversity is our weakness.
Over time, America's ability to receive immigrants over a long period of time has proven to be advantageous, particularly when these groups of immigrants were absorbed into American culture. It gave us our character and our strength was in the unification under an "American Culture".
It was the cultural phenomenon of "PC" which tore those common bonds assunder and detroyed the American identity, "of many cultures, one people". Now it's "of many cultures, and just about all of them are whining ingrates with no sense of what America stands for".
I haven't even an idea of what to suggest until we at least close the borders and round up the illegals, but it will take another disaster with thousands of casualties before that idea sinks in. By then it will be too late.