Complex sentence: The Flag of Nakhichevan is officially that of Azerbaijan, but there was one used in 1991 by separatist groups in Nakhichevan during the breakup of the former Soviet Union.
Split into simpler sentences: The Flag of Nakhichevan is officially that of Azerbaijan. However, another flag was used in 1991 by separatist groups in Nakhichevan during the breakup of the former Soviet Union.