For some who believe this issue has also recently exploded due to Obama might also want to read up on NAFTA and the long term effects. This is a rather older artice but I think it still shows some of the effects we are seeing even now:
Illegal Immigration and NAFTA | Economy In Crisis
One of the largely overlooked aspects of the North American Free Trade Agreement is the fact that the failed trade pact has been the catalyst for the massive increase in illegal immigration over the past two decades or so.
An influx of highly subsidized corn flooding the Mexican market has displaced millions of rural farmers, according to McClatchy Newspapers. Prior to the implementation of NAFTA, Mexican officials claimed that factory jobs would fill the void left by disappearing work on family farms.
Mexican officials had promised that NAFTA would result in the “export of goods, not people.” That, however, has turned out to be far from reality.
Since NAFTA was signed into law, illegal immigrants in the U.S. has increased to 12 million today from 3.9 million in 1993, accounting for an overall increase of over 300 percent. According to the Pew Hispanic Center, 57 percent of those entering the country illegally are from Mexico.