The Mexican government says nearly 23,000 people have died in drug-related violence since a military crackdown on cartels began in 2006.br br That announcement comes as officials face a new front in their war against the drug gangs.br br Two of Mexico's most powerful cartels have joined forces to battle government security forces as well as a third cartel seeking its own slice of the cross-border drug trade.br br Al Jazeera's Mariana Sanchez reports from Mexico City (14 April 2010).