The phrase, "poor mexico: so far from god, so close to the united states," refers to what reality?

The phrase actually refers is the what by now should be the well-known history of the U.S. supporting military coups all over South and Central America. Many of the officers involved in the coups with documented violation of human rights were trained by the U.S. in the so-called School of Americas renamed the Western Hemisphere for Institute for Security of Cooperation. 
If you look back at the history of the U.S, you'll see a number of wars or otherwise extensive conflicts averaging every 20-30 years. This rabid aggression and the use of extensive deception are among the reasons U.S. presence is not only resented in Central/South America but currently in areas such as the Middle East.

Hope this helped! :)