New Delhi, Feb. 23 -- The Mexican army killed the leader of the Jalisco New Generation Cartel, Nemesio Ruben Oseguera Cervantes, "El Mencho," on Sunday, decapitating what had become Mexico's most powerful drug cartel and thrusting swaths of the nation into chaos.

The drug lord was the Mexican government's biggest prize yet to show the Trump administration in its efforts to crack down on the cartels, and his death was met with a forceful reaction from the cartel, known by its Spanish initials CJNG.

Cars burned out by cartel members blocked roads at more than 250 points in 20 Mexican states, authorities said, and left smoke billowing into the air. Jalisco's capital, Guadalajara, was turned into a ghost town Sunday night as civilians hunke...