Complex sentence: Arturo Beltrán and Alfredo Beltrán had met with top members of Los Zetas in Cuernavaca, where they agreed to form an alliance to fill the power vacuum.
Split into simpler sentences: Arturo Beltrán and Alfredo Beltrán had met with top members of Los Zetas in Cuernavaca. There they agreed to form an alliance to fill the power vacuum.