Complex sentence: A rally in Istanbul commemorating the twentieth anniversary of the 1992 massacre of Azerbaijani civilians by Armenian and CIS forces (of former Soviet republics), turned into an Anti-Armenian demonstration containing hate speech and threats towards Armenians.
Split into simpler sentences: A rally in Istanbul commemorating the twentieth anniversary of the 1992 massacre of Azerbaijani civilians by Armenian and CIS forces (of former Soviet republics). Some elements of the crowd turned it into an Anti-Armenian demonstration containing hate speech and threats towards Armenians.