It began in 1965 with Ted Kennedy's "Family Reunification Act" where any individual immigrant could bring his relatives. Kennedy bastardized (literally) a perfectly good program.
Prior to that an immigrant or Alien went through a naturalization process by having an American "sponsor" who aided him in finding and KEEPING a job. Yes, that's right... if he was fired, or commited a crime, he could well be deported. It was alot like being on probation. Also, the immigrants were from Eastern Europe and had a strong work ethic, worked hard and paid taxes.
Compare that to a mom on a burro with an "anchor baby".... if you dare..... Now you're ready to read "Alien Nation" by Peter Brimelow.