Mexico broke international law with the cartels and Americans suffer the consequences

Mexico has handled the cartels so poorly that it broke international law. It is obligated to prevent the harm cartels are creating through drug and human trafficking. It didn't do it.

In failing to implement and enforce robust security measures, Mexico is abdicating its responsibility to prevent cross-border harm — a breach of the non-intervention principle enshrined in international law. 

By allowing so much harm to America and its citizens to emanate from Mexico, the Mexican government is violating international law by failing to rein in the criminal enterprises at the heart of the illegal trafficking. A careful analysis of international legal principles, state responsibility and treaty obligations makes it clear that Mexico is neglecting its duty to prevent harm emanating from its territory (International Law Commission, 2001).