For example, Monterrey and Nuevo León in general has always been fairly calm and it is a major hub globally for automotive, power electronics, and machining.
Most of the rise of criminalization in Mexico can be tied to the economic crises of the 1994-96 (peso crisis), 2001-03 (factories moving from Mexico to China), 2008-09 (collapse of automotive industry in the US, and then COVID (8.3% GDP contraction - one of the worst globally).
Whenever the Mexican economy recovers, criminality tends to recede.