If you want to understand today's immigration policy quagmire, you need to understand the Immigration Reform and Control Act, known as IRCA, a landmark piece of legislation signed by President Ronald Reagan on November 6, 1986.
After much political wrangling over its provisions, the measure did two key things: First, it provided close to 3 million undocumented immigrants a path to legal status, drastically changing their economic prospects and allowing them to move freely about the country and settle in non-traditional receiving states, including in the South and Midwest. Second, in exchange for the amnesty provision, the program set in motion a trend toward tighter enforcement, at the border and in the workplace. The workplace component made it officially illegal to hire undocumented workers, although loopholes in the law allowed employers to continue hiring them, a situation that has led to the current debate over the federal E-Verify program.
This paper published today by the Migration Policy Institute does a good job of explaining IRCA and its legacy 25 years later; one of its three authors is Doris Meissner, who directed the now-defunct Immigration and Naturalization Service during the Clinton administration. An excerpt: