From Wikipedia:
The song was inspired by a day trip the band members (Boon, bassist Mike Watt, and drummer George Hurley) had taken to Mexico on the Fourth of July, 1982. (The same trip also inspired the Mike Watt composition "I Felt Like A Gringo" on Buzz or Howl Under the Influence of Heat.) Moved by some of the more downtrodden elements of the area that he had seen, D. Boon set about writing a song in sympathy with the people of Mexico.
From Wikipedia: The song was inspired by a day trip the band members (Boon, bassist Mike Watt, and drummer George Hurley) had taken to Mexico on the Fourth of July, 1982. (The same trip also inspired the Mike Watt composition "I Felt Like A Gringo" on Buzz or Howl Under the Influence of Heat.) Moved by some of the more downtrodden elements of the area that he had seen, D. Boon set about writing a song in sympathy with the people of Mexico.