The leader of one of the world's most dangerous drug cartels is dead, and the ripple effects are already being felt on both sides of the U.S.–Mexico border.

Nemesio Oseguera Cervantes — known as "El Mencho" — was killed Sunday by Mexican military forces near Tapalpa, in his home state of Jalisco. Mexican Defense Secretary Ricardo Trevilla said authorities tracked Oseguera Cervantes to his hideout by following one of his romantic partners. He and two bodyguards fled into a wooded area, where they were seriously wounded in a firefight. All three were taken into custody and died en route to Mexico City.

The Jalisco New Generation Cartel (CJNG) — the criminal empire Oseguera Cervantes built into one of Mexico's fastest-growing drug networks — responded immediately with widespread violence. Security Secretary Omar García Harfuch confirmed that 25 members of the Mexican National Guard were killed in six separate cartel attacks. At least 30 criminal suspects were killed in Jalisco, and four others died in neighboring Michoacán. A prison guard and a state prosecutor's office agent were also killed. In total, authorities reported at least 73 deaths across the country tied to the operation and its violent aftermath.

Mexican authorities said cartels erected more than 250 roadblocks across 20 states and set fire to vehicles. Several Mexican states canceled school Monday as the government worked to restore order. By Monday afternoon, officials said all roadblocks had been cleared. Mexican President Claudia Sheinbaum urged calm as military patrols fanned out across the country.

For San Diego, El Mencho's death marks a pivotal — if uncertain — moment. The CJNG was the dominant cartel trafficking fentanyl, methamphetamine, and cocaine through the Tijuana corridor and across the San Ysidro and Otay Mesa ports of entry, which together handle more vehicle crossings than any land border in the world. The White House confirmed that U.S. intelligence agencies supported the Mexican military operation, and applauded Mexico's army for taking down one of the most wanted criminals in both countries.

While El Mencho's death removes the cartel's founding leader, law enforcement experts warn that major cartels rarely collapse after losing their boss — and a leadership vacuum often triggers internal power struggles that can temporarily increase violence near the border. San Diego County residents and border communities should expect heightened security presence and possible travel disruptions in northern Baja California in the days ahead as the situation stabilizes.