Complex sentence: The Soviet coup d'état attempt on 19 August 1991 became the spark for the so-called Chechen revolution: on 21 August the NCChP called for the overthrow of the Supreme Soviet of the Chechen-Ingush Republic.
Split into simpler sentences: The Soviet coup d'état attempt on 19 August 1991 became the spark for the so-called Chechen revolution. On 21 August the NCChP called for the overthrow of the Supreme Soviet of the Chechen-Ingush Republic.