Ioan Grillo, head of CrashOut Media, said that "foreign mercenaries" increase violence and specialized tactics in what he refers to as the "Mexican Cartel War." He made this statement in a commentary for Substack on October 18.

"Foreign mercenaries throw oil on the already blazing fire of the Mexican Cartel War," said Grillo, Mexican cartels media specialist. "They bring experience from other battlegrounds and knowledge in battle tech, from car bombs to improvised land mines."

According to CrashOut Media, the United Cartel from Michoacán, Mexico, and their rival, the Jalisco Cartel, hire mercenaries from foreign countries and gangsters to assist their efforts against one another. Colombian mercenaries are often used to introduce and teach military tactics to the cartels’ sicarios.

Yahoo News reports that in 2016, the Colombian government and FARC (Revolutionary Armed Forces of Colombia), the largest rebel group, agreed to a peace deal. Many fighters on both sides, whether government soldiers or guerrilla fighters, became unemployed and began working for the Mexican drug cartels. In 2021, it was reported that one group of the United Cartel employed 26 Colombian fighters. A separate group paid 10 Colombians $600 per week to provide information about the Jalisco Cartel.

The tactical use of landmines is new to the cartels’ war and is attributed to these Colombian mercenaries. Tim Sloan, a U.S. official based in Mexico City, said: "Homemade mortars, land mines, bomblets dropped by drones — all that technology was brought up by former FARC members working mainly with CJNG."

Mercenaries from Guatemala, Honduras, and El Salvador have also assisted cartels. There is also a history of U.S. army veterans being recruited by the cartels and traveling to Mexico to fight in these wars.

Grillo is an author and cartels specialist located in Mexico. According to his Substack profile, he specializes in crime, drugs, and the politics of the cartels.