ROBERT NEUSTADT: The North American Free Trade Agreement, which was signed in 1994, is the biggest single economic factor that caused undocumented migration from Mexico to the US to “explode.” Prior to NAFTA, Mexico was a corn exporting country. It is important to understand that corn is central to Mexican culture. This goes beyond the fact that tortillas are a food staple–according to the Mayan creation myth, human beings were made from corn. After NAFTA was signed, the US started exporting US government-subsidized corn grown by industrial farms to Mexico. Mexican farmers with small milpas (corn plots) could not compete. The price of corn dropped 75% and millions of small and mid-sized Mexican farmers lost their land. This rippled outward to those who processed corn, transported corn, made tortillas and ate tortillas. I don’t think it’s a coincidence that we started constructing walls on the border the same year that NAFTA was signed.