What is the importance of Mexico in the nonfiction book, Underground America: Narratives of Undocumented Lives?

Many of the interviewees in Underground America comes from Mexico—from states such as Jalisco, Oaxaca, and Michoacán. The majority of the interviewed Mexicans working in the United States cross the border by foot, although a small minority crosses with proper papers via plane. They are predominantly in search of greater economic opportunities and plan to send much of the money they make home.