When Americans think about the border, they tend to picture undocumented workers or clandestine river crossings. They don’t think about war. But what’s happening in Mexico now is a war—no other word seems suitable—and the most gruesome battles are taking place within miles of the U.S. So far this year, more than 1,350 people have been murdered in drug-trafficking-related crimes in Mexico. Last year, according to tallies kept by Mexican newspapers, 2,500 people died; since 2001, the number is close to 10,000—twice the number of American soldiers killed in Iraq and Afghanistan.

These killings have become such an everyday part of life that there’s a special word for them: narcoejecuciones, or narcoexecutions. The murdered include police, judges, prosecutors, soldiers, reporters, politicians, and innocent bystanders. Shootouts in broad daylight, mass executions, and public assassinations have become routine. “The old narco gunman was a guy with a gold tooth and a .45, and if you lost a load of drugs, he’d send someone out there to plug you,” says J.J. Ballesteros, a veteran A.T.F. agent in Texas. “The phenomenon we’re looking at today is entirely different. Now we have paramilitary cells with military training challenging one another and the government.”

There are, in fact, two drug wars raging in Mexico. One is between drug-trafficking organizations—in particular, the Sinaloa cartel and its main rival, the Gulf cartel—over control of smuggling routes to the U.S. The belligerence is easily understood, given the stakes. The U.S. government estimates that the cross-border drug trade was worth as much as $25 billion last year. According to Mexico’s attorney general, Eduardo Medina Mora, $10 billion worth of drug proceeds crosses from the U.S. into Mexico each year in the form of bulk cash. The Sinaloa cartel, which controls much of the northwest border region, is led in part or in whole by Guzmán, who has lived on the run since 2001, when he escaped from prison aboard a laundry truck. The Gulf cartel, which reigns in the northeast, was headed by Osiel Cárdenas Guillén until his extradition to the U.S. in early 2007.

The other war is between the government and the cartels. Mexican presidents have pledged to end trafficking before, but Calderón, who took office in 2006, seems, in contrast to his predecessors, to be sincere, and his policies are having some effect. He has dispatched tens of thousands of troops, locked up hundreds of traffickers, and undertaken sweeping reforms of the police and judiciary. With each salvo, however, the violence intensifies. The wars aren’t just Mexico’s problem, either. The U.S., with less than 5 percent of the world’s population, consumes more than half of the world’s drugs; most of the marijuana and methamphetamine, much of the heroin, and 90 percent of the cocaine comes from or through Mexico. “U.S. consumers are already financing this war,” Medina Mora tells me, “only it’s on the wrong side.”

In late 2007, the Bush administration, which counts Calderón as one of its few friends in Latin America, announced the Mérida Initiative. If passed by Congress, it will provide Mexico with $1.4 billion in equipment and training over three years. But the initiative, with its unprecedented outlay of funds, is fraught with contradictions, since it would go to fight the flow of weapons coming in illegally from the U.S. More than 90 percent of the A.T.F.’s traces of guns seized in Mexico lead to the States. The Mexican ambassador recently estimated that 2,000 guns cross the border every day. Even if that figure is halved, it’s a trade worth hundreds of millions of dollars a year.

In January, a week after Beltrán Leyva’s arrest, I visit the A.T.F.’s field office in Phoenix to speak to Bill Newell, one of four special agents in charge of the border region. “The Mexicans and the Colombians, they’re very similar in the following respect,” says Newell, who cut his teeth in Colombia in the 1990s and speaks fluent Spanish. “They will fight to the death to protect their source and supply of drugs and their trafficking routes.”