The great city split into 3 is the built-up personality breaking apart under the fire of awakening, body and soul and spirit divided out as the self of a lifetime comes undone. The number 3 marks that threefold nature laid open. The lesser cities are the habits and clusters of thought that fall when the ruling mind collapses.
Babylon is the confused lower mind, the mixture of desire and false belief a person exalts like a proud metropolis. The cup of wrath is the concentrated inner force returning on that mixture, one's own accumulated confusion drunk to the bottom until the false city cannot stand.
The great city: the built-up personality, the whole proud structure of the self raised over a lifetime
Babylon: the confused lower mind, the mixture of desire and false belief a person exalts like a metropolis
The cities of the nations: the lesser habits and clusters of thought that fall when the ruling mind collapses
The cup of wine: the concentrated inner force returning on the false self, the reckoning drunk to the bottom