This flag has been the flag of various Afghan rulers:
Flag of Zengid dynasty and Flag of Afghanistan (pre-1901) and the flag of the Black Guards.
This flag has also been the flag of the Sadozai Sudhan rulers of Sidhnuti

This can be used to represent the Abbasid Caliphate, since while the concept of rectangular national flags did not exist during Abbasid times, black was the dynastic color of the Abbasids and the "black banner" of the Abbasids is famous in Islamic history. It was also used by many Islamic dynasties in different regions of the world till the late 19th century. It is also used by anarchist groups and pirates.
Own work
PavelD