From the International Herald Tribune:

These days, it is easy to form the impression that a war is going on in Mexico. Thousands of elite troops in battle gear stream toward border towns and snake through the streets in jeeps with 50-caliber machine guns mounted on top, while fighter jets from the Mexican Navy fly reconnaissance missions overhead.

Gun battles between federal forces and mobsters carrying rocket-propelled grenade launchers have taken place over the past two weeks in border towns like Rio Bravo and Tijuana, with deadly results.

Yet what is happening is less a war than a sustained federal intervention in states where corrupt municipal police officers and drug-cartel members have worked together in relative peace for decades, officials say. The federal forces are not only hunting cartel leaders - they are also going after their crews of gunslingers, like the Zetas, who terrorize the towns they control.

The illegal drug trade in Mexico is a $23 billion industry. Around 2,500 people were killed last year in drug related homicides.