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