The fundamental force which drives all human activity is basically selfish. Its sole aim is to provide for and to protect self. But sadly, this force does not restrict itself merely to acquiring adequate provision for self. It drives one to strive for gain without limit - far beyond one's actual needs and without regard for how this may be depriving others.
The agent of disparity is therefore the inherent selfishness within human nature. This is the engine which powers the process through which wealth is systematically drained from the unfortunate many by the fortunate few.
Individual human selfishness powers the process by which disparity is generated. But it is a blind force and it is present in everybody. Therefore it cannot of itself determine which particular individuals shall be members of the fortunate few and which shall not. It may well power the process, but it cannot initiate or control it.
This is done by a socio-economic system based on rules and protocols which facilitate the selfishness of arbitrary individuals who are selected for privilege by the fickle frolics of chance and caprice.