Immigration into the United States fluctuated throughout the 20th century because of varying economic conditions. But the changes made by the Immigration Reform and Control Act of 1986 drastically increased the number of immigrants allowed into the United States. This in turn has had a negative impact on the quality of life of many Americans today due to the mass increase in population.
Worse, the United States has mass illegal immigration because successive Congresses and Presidents have decided they want it. In one action after another over the last decade, they have declined to approve measures known to be effective to slow the flow of illegal immigrants, they have decided to end various kinds of enforcement that had been effective, and they have approved a series of rewards to those who violate immigration laws.