CIUDAD JUAREZ, Mexico — If Dante had ever been to Juarez he would have placed it squarely in the seventh circle of hell, the one housing “violence” and “ringed by a river of boiling blood.”

The city, which lies on the Rio Grande just across from El Paso, Texas, is the murder capital of the world, claiming more than 5,500 killings since January 2008. It is responsible for one-fifth of the more than 25,000 drug-related murders that have occurred in Mexico since 2006 when President Felipe Calderon officially declared war on the country’s heavily armed drug cartels.

That national war reached another dramatic turning point last month when the front-running candidate for governor in a drug-torn Mexican border state was assassinated by gunmen believed to have been sent by a drug cartel.

Nowhere is the violence more horrific than in Juarez, where 13 teenagers were murdered at a partyand 17 recovering drug addicts killed at a rehab center.

But amid all the media spotlight on this butchery, the facts of who exactly is fighting, who is dying and why remain misty and confusing to many observers.

In this special report, “The Seven Circles of Juarez: The murder capital of the world and those who dwell in its unique hell,” GlobalPost features a series of videos and dispatches that explore the concentric rings of greed, lust, avarice and complicity that have made the town its own, living inferno. We also look at the human stories of the paramedics, priests and social workers trying to pull the city up from the fiery depths.

Here’s a quick primer on the conflict. We hope it provides a way to navigate down into the reality and the complexity of life in Juarez.

Is Ciudad Juarez really the most murderous city in the world?

Most sources, including the FBI and various non-governmental organizations, find that it is. In 2009, Juarez had 191 homicides for every 100,000 inhabitants, according to Mexico’s Citizen Council for Public Security. In second place was San Pedro Sula, Honduras, with 119 killings. New Orleans, America’s most murderous city, had a rate of 69 killings, putting it in eighth place. The United States as a whole has an annual murder of about 5 per 100,000. Of course, many homicides both in Juarez and around the world are never reported.

Who is fighting in Juarez?

According to both Mexican and U.S. agents, the conflict exploded in January 2008 when the Sinaloa Cartel, led by Joaquin “Chapo” Guzman went to war with its old partners in the Juarez Cartel, led by Vicente Carrillo Fuentes, for control of the city. To fight this war, the Juarez mob recruited a street and prison gang called the Barrio Azteca while the Sinaloa Cartel recruited a rival gang called the Artist Assassins, or Double A’s. The alignment of these thousands of street gang members backed by the money and armed with weapons smuggled from the United States, has led to a major proliferation of the violence.

What are the cartels fighting over?

The main bounty of Juarez is its position for smuggling narcotics into the United States. Located in the center of the 2,000-mile U.S.-Mexico border, Juarez has long been a strategic treasure for moving cocaine, heroin, marijuana and crystal methamphetamine toward American users. The gangsters who control this “plaza” can not only move their own drugs but tax other smugglers 20 percent to move their goods through the corridor. Furthermore, the Juarez plaza includes both the international bridges in the city itself and the ports and open desert that stretch out into the Juarez Valley. In total, it is worth billions of dollars.