Ciudad Juarez, on the Mexico-US border, is one of the world's most violent cities.

BBC: Mexico prison shooting: 17 dead in Ciudad Juarez clash

Most of the counties and cities on America's southern border are poor, with correspondingly wretched schooling and health care.

ECONOMIST: The colonias of the Mexican border

These are two conjoined cities whose economies depend on the imbalances created by the national border than runs along the river that marks the border.

FORBES: Why Is Mexico's Murder City Attracting Investors?