Drawing on extensive interviews with subnational elites and focusing on six Mexican states (Baja California, Chihuahua, Jalisco, Nuevo León, Michoacán, and Guerrero), this chapter analyzes how party alternation and opposition governors’ decisions to remove top- and mid-level officials in the state attorneys’ offices and the state judicial police led to the breakdown of informal government protection networks for drug cartels in the 1990s and early 2000s. Cartels created private militias in response to this political uncertainty in Mexico’s gray zone of criminality, which allowed drug lords to defend their turf and challenge rival territory. Using a sequential analysis, we show how every new party alternation, starting in Baja California in 1989 up to Guerrero in 2005, stimulated an arms race among cartels and led to the proliferation of increasingly lethal dyadic conflicts in the northwest, northeast, and south of the country. By 2006, Mexico’s drug trafficking industry had experienced dramatic transformations: cartels used powerful private militias to settle disputes and the death toll surpassed the 1,000 murders threshold used to classify a conflict as a civil war.