The villain here was the Hate-Monger, who was leading a group of high technology-powered Nazis that were killing immigrants, (or would-be immigrants), near the U.S./Mexico border in the Sonoran desert. This was very important because, around the same time, there was a lot of controversy at the Arizona border due to "The Minutemen," armed militia groups who had taken it upon themselves to "patrol" the U.S./Mexico border.
In the story, instead of Minutemen, they are Nazis, which is essentially what they are, and exactly why I like the story so much--because they truly are villains! (Not heroes, or patriots, or whatever someone else might come up with to dress it up).
Frank Castle, the Punisher, does not like what these Nazis are doing. And although he usually spends his time taking out mob bosses or super-villains, he decides to infiltrate them so to best kill them. Although most of the story is about how Frank goes about infiltrating the Nazi camp and the repercussions of that, the beginning of the story does shed some light on some of the reasons why people go come to the U.S. from Mexico. In one whole page, Staurt, (a sort of sidekick to Frank), reads him some information, including this passage:
"Maquilas or maquiladoras, depending on your grasp of Spanish, exist throughout Mexico and Latin America in these--these special zones. No tariffs or taxes. They bring raw goods in and ship finished crap out. They're...dictatorial sweatshops, basically. NAFTA-sanctioned sweatshops."
I like this story so much that I even went ahead and bought a hardcover collected trade and recommend the same to anybody who is looking for a good story. As long as you don't mind a little violence.