Much has been made of the risks Mexico’s drug war poses to tourists, but the most immediate threat is to Mexicans themselves, who are increasingly having to share their cities with criminal cartels.

Keith Boag's documentary, Mexico at War, appears tonight on CBC's The National at 10 p.m. (10:30 NT) on CBC-TV and 9 and 11 p.m. ET/PT on CBC News Network.

As part of a weeklong series on the effects of the Mexican drug war, CBC News travelled to Monterrey, a city of four million people in the prosperous northeastern state of Nuevo León.

This cosmopolitan area is home to the biggest Mexican companies and hundreds of multinationals, and boasts the highest per-capita income of any city in Mexico.

After the Zetas drug cartel fire-bombed the Casino Royale in Monterrey, killing 52 people, Mexican President Felipe Calderon, pictured, denounced the unrelenting U.S. demand for drugs. (Ronaldo Schemidt/AFP/Getty Images )

In recent years, it has also become a home for the Zetas, the domestic drug cartel notorious for its assassinations and bombings.

The Economist magazine reported that the rate of drug-related murders in the Nuevo León region had increased by 193 per cent from 2010 to 2011, owing largely to attempts by the Sinaloa drug cartel to oust the Zetas from Monterrey.

Alfredo Corchado, a Mexican-born American journalist who has covered the drug war for nine years, worries that the Zetas’ penetration of Monterrey will have repercussions for the entire nation.

"If we lose Monterrey, basically we lose the country," Corchado told CBC News.

Escalating drug activity

Mexico has been involved in drug production and distribution for decades, but its role as a supplier has grown considerably in the 2000s. It is the main foreign purveyor of marijuana and methamphetamine to the U.S. and the chief transit route for the country's cocaine and heroin.

Increased drug traffic has led to a proliferation of cartels and vicious turf battles.

Upon taking office in 2006, President Felipe Calderon launched a government offensive to stanch the burgeoning violence. Since then, almost 50,000 people have died – most of them involved in the narcotics trade – and the drug war shows no signs of abating.

Monterrey’s wake-up call was the fire at the Casino Royale in August 2011. The blaze started after members of the Zetas doused the hotel entrance with gasoline and lobbed in a grenade. Their apparent motive: an unpaid extortion fee.

The fire claimed the lives of 52 people, most of them innocent bystanders, and was the bloodiest crime in Monterrey’s history.

In the immediate aftermath, Calderon vented his anger on the U.S. He claimed that a steady supply of American guns and the U.S. appetite for recreational drugs is sustaining the cartels.

"The economic power and firepower of the criminal organizations operating in Mexico and Latin America come from this endless demand for drugs in the United States," he said.

It is widely held that one of the reasons Calderon’s drug war is not achieving its goals is because Mexican police are being coerced or corrupted by the cartels.

During a riot at Monterrey’s Apodaca Prison in February 2012, members of the Zetas murdered 44 members of the rival Gulf cartel. Thirty Zetas members managed to escape.

Investigators say the riot couldn’t have happened without the complicity of prison guards and administrators.

Marines in hot pursuit

With citizens and many police too terrified to take on the gangs, Mexico is increasingly relying on the military to root them out. Marines wearing masks to hide their identities roam the cities and countryside in search of wanted Zetas operatives such as Oscar Manuel Bernal, also known as "the Spider."

P.O.V. In many ways, Canadians are deeply linked to events in Mexico, be it through trade, travel or personal ties. When you watch reports about the violence in Mexico, do you see your experience reflected? What is your story of Mexico?

"We don’t feel frustrated. We simply understand Mexican society and the existing fear. These groups threaten to kidnap or kill anyone who gives out information on them," one Marine captain told CBC News, insisting that the military can win this war.

Mauricio Fernandez, the mayor of San Pedro, a wealthy municipality suburb of Monterrey, has found his own methods to fighting the war.

Fernandez pays for information on the Zetas’ activities, and levies high municipal taxes in order to fund a well-armed, highly competent police force.

He’s been able to keep San Pedro’s neighbourhoods reasonably safe, and thwarted numerous attempts on his own life.

"So far, the four guys who have mentioned that they were planning to kill me, well, they are dead, fortunately," said Fernandez. "So right now the score is four to zero."

Formulating a new national strategy to defeat the drug gangs will be a major issue in the Mexican general election in July. Corchado believes the Zetas may actually increase their violent activity in order to send a cautionary message to any presidential candidates hoping to stamp them out.

"We debate this as journalists: Is it an insurgency? Is it terrorism? Is it an old-fashioned drug war?" said Corchado.

"But in the end, what we see on the streets is people dying."