who were bandagans and how did their appointment create political instability ?

many delhi sultans needed reliable governers. rather than appointing landed chieftains aristrocats and rich landlords the early rulers especially iltutmish posed the special slaves purchased for military services called bandagans in persion.the khaljis and tughluqs continued using the bandagans and also raised people of humble birth, who were often their clients,to high political position. they were appointed as generals and govereners. however this introduced an element of political instability.