There are only four ways in which a ruling group can fall from power. Either it is conquered from without or it governs so inefficiently that the masses are stirred to revolt or it allows a strong and discontented Middle group to come into being or it loses its own self- confidence and willingness to govern. These causes do not operate singly and as a rule all four of them are present in some degree. A ruling class which could guard against all of them would remain in power permanently. Ultimately the determining factors is the mental attitude of the ruling class itself