U.S. military assessment expressed concern that the war could cause a “rapid and sudden collapse” of the Mexican government

Fighting between rival drug cartels began in earnest after the 1989 arrest of Miguel Ángel Félix Gallardo who ran the cocaine business in Mexico. There was a lull in the fighting during the late 1990s but the violence has steadily worsened since 2000. Former president Vicente Fox sent small numbers of troops to Nuevo Laredo, Tamaulipas, on the US-Mexico border to fight the cartels with little success. It is estimated that about 110 people died in Nuevo Laredo alone during the January-August 2005 period as a result of the fighting between the Gulf and Sinaloa cartels. In 2005 there was a surge in violence as a drug cartel tried to establish itself in Michoacán. Although violence between drug cartels has been occurring long before the war began, the government held a generally passive stance regarding cartel violence in the 1990s and early 2000s. That changed on December 11, 2006, when newly elected President Felipe Calderón sent 6,500 federal troops to the state of Michoacán to put an end to drug violence there. This action is regarded as the first major retaliation made against the cartel violence, and is generally viewed as the starting point of the war between the government and the drug cartels. As time progressed, Calderón continued to escalate his anti-drug campaign, in which there are now well over 25,000 troops involved.

In April 2008, General Sergio Aponte, the man in charge of the anti-drug campaign in the state of Baja California, made a number of allegations of corruption against the police forces in the region. Among his allegations, Aponte stated that he believed Baja California’s anti-kidnapping squad was actually a kidnapping team working in conjunction with organized crime, and that bribed police units were being used as bodyguards for drug traffickers. These accusations of corruption suggested that the progress against drug cartels in Mexico have been hindered by bribery and corruption.

On April 26, 2008, a major battle took place between members of the Tijuana and Sinaloa cartels in the city of Tijuana, Baja California], that left 17 people dead. The rival cartels are using not only handguns, but semi-automatic weapons such as variants of the AK-47 and AR-15 purchased in the United States. The battle also brings about concern about the violence spilling into the United States, as Tijuana and a number of other border cities become hotspots for violence in the war.
In September 2008, grenade attacks in Morelia by suspected cartel members killed eight civilians and injured more than 100.In January 2009, a U.S. military assessment expressed concern that the war could cause a “rapid and sudden collapse” of the Mexican government due to the military strength of organized crime.