Tijuana, pressed up against the US border, shares with San Diego one of the most heavily trafficked land borders in the world.

Tijuana’s location and infrastructure have made it coveted territory for Mexico cartels vying to feed the US’s voracious appetite for illegal narcotics.

The Sinaloa cartel, guided to dominance by Joaquín “El Chapo” Guzmán, has held control of the city since the end of last decade, and that control had helped keep homicides below their cartel-war peak.

But the Jalisco New Generation cartel, a relatively new organization ascendant on Mexico’s narco scene, arrived in Tijuana over the last two years.

The CJNG has joined with remnants of the Arellano Felix Organization, which dominated Tijuana prior to the Sinaloa cartel’s arrival, to form a new, local criminal group and challenge Sinaloa’s hold over Tijuana.

In a city where the reduction of drug-war violence has been seen as a “miracle,” the simmering cartel clash has pushed deadly violence to new levels, bringing grisly reminders of a period the city had put behind it.

Mexico Tijuana drug violence shootout policeForensic officers and policemen work in the area where 15 men were killed in one of the deadliest shootouts in Mexico’s then three-year-old narco-war, Tijuana, April 26, 2008.REUTERS/Stringer