On December 10 1991 , a referendum held in the NKAO and the neighboring Shahumian region resulted in a declaration of independence from Azerbaijan as the Nagorno-Karabakh Republic . On December 10 , 1991 , as the Soviet Union was dissolving , a referendum held in the NKAO and the neighboring Shahumian region resulted in a declaration of independence from Azerbaijan as the Nagorno-Karabakh Republic .