With their leaders dead or in jail, Mexico's drug cartels have splintered into hundreds of factions battling for dominance and raising the level of violence in Mexico, respected journalist and author Juan Alberto Cedillo told EFE.

"The breakup of the big cartels led to a criminal insurgency, because once these gangs were left without leaders and without the money they made from the sale of drugs, they turned to attacking society in general," he writes in his latest book, "Las Guerras Ocultas del Narco" (The Hidden Drug Wars).

Cedillo, 64, says this narco-insurgency has taken over villages and municipalities and has "trickled like water into any business where corruption reigns."

In the book, he says the breaking point came with the battle launched by the Sinaloa cartel in 2004 against the Gulf cartel and its armed branch, Los Zetas, for control of Nuevo Laredo, just across the border from Laredo, Texas.

"The battle for Nuevo Laredo set off the war of the cartels. In 2006, (then-President Felipe) Calderon launched his policy of sending the army to wipe out the drug traffickers, which only increased the violence," he said.

Nuevo Laredo turned out to be a strategic channel for the cartels, through which some 75 percent of the terrestrial drug trade was sent from Mexico to the United States. The battle to control it left more than 2,000 dead.

The border city was turned into "a laboratory where the cartels became paramilitarized with small armies of hired killers, and where grenades and heavy weapons appeared as did bodies that had been decapitated, quartered and burned," Cedillo said.

The official strategy of combating drug trafficking, focused on catching the drug lords, split up the cartels and left "thousands of cells without leaders."

In that way, criminal groups like Los Zetas, an organization founded by Mexican special forces veterans that dominated the northeastern part of the country between 2001-2004, went from being an extremely disciplined unit to dozens of disorganized factions.

The violence generated by the war among Mexico's drug cartels has left more than 200,000 people dead and 30,000 missing over the last 12 years.

During the same period, authorities captured a long list of drug lords, most prominently Joaquin "el Chapo" Guzman, a reputed billionaire who is now awaiting trial in the United States.

Several other crime bosses died in shootouts with security forces, including the man thought to have founded Los Zetas, Heriberto "el Lazca" Lazcano.