Los Zetas appears to be one enemy that the United States did in fact help create:

The U.S. Justice Department is warning local police in Arizona and California a group of rogue Mexican military commandos may be headed this way. They're thought to be setting up new drug smuggling routes and it could bring new violence to the border area.

They are elite "special forces" of the Mexican military trained in the U.S. at the School of the Americas at Fort Benning, Georgia and sent to "wipe out" one of the most powerful Mexican drug cartels.

But these soldiers deserted and became the muscle for the very cartel they were supposed to destroy.

The date on the story is June 3, so it's a couple weeks old but still valid. Zeta-like drug running commandos have been working the border region for quite a while:

The Intelligence Bulletin we obtained says the Zetas are responsible for hundreds of violent drug-related murders. It says they've executed journalists, murdered people in Dallas, McAllen and Laredo, Texas. They even detained two DEA agents and recently they've shot at Border Patrol agents. At the Arizona border with Mexico agents are already seeing a major increase in violence.

Jose Garza says, "Last year we had documented only nine shootings against our agents. This year we're up to about 18 shootings already."

Agent Jose Garza says his agents have seen no direct evidence the Zetas are responsible for the shootings here, but as far back as three-years ago, the Zeta-like tactics started to appear.

In March of 2002, U.S. Customs agents were involved in a shootout south of Phoenix with an enemy they had not seen before. Equipped with automatic weapons, body armor, and state-of-the-art communications, in a word - it looked "military."

Just this year we have seen shootouts between the federal and local police in Nuevo Laredo, near Laredo, Texas, an assination of NL's police chief just six hours after he took office, and now we have an elite commando squad butching up the already violent Mexican drug cartels. Never mind the very real terrorist threat for a second--we need to get some control over the border just to make a dent in drug-related crime and violence. That crime and violence can and often does spill across the border deep into the US.