Babylon is the confused lower mind of a person, the inner city of mixed and warring thoughts built up over a lifetime of living in the senses, and its fall is the collapse of that whole disordered mental world when the higher light rises. Its very name carries the confusion of tongues, the scattered voices that never agree within a divided man.
The devils and foul spirits are the base impulses and the birds are the flighty restless thoughts that nest and circle in an unclean mind. When the sensual lower nature finally breaks down, all the dark impulses and scattered thoughts it once housed are exposed as the tenants they always were.
Babylon: the confused lower mind, the inner city of mixed and warring thoughts built over a lifetime
Devils and foul spirits: the base sensual impulses that inhabit the lower nature
Unclean birds: the flighty restless thoughts that nest and circle in a darkened mind