Powers created by worldliness and sin are crumbling, as they well may; "the city of God remaineth!"
This idea, which has underlain all Christian philosophy of history, from the first apologists who prophesied the fall of the Empire and the coming of the millennium, down to our own day, received its classic statement in St Augustine's City of God.
If "the idea of humanity," as Kant called it, has ethical perfection at its core, then a universe which is really an organic whole must be ultimately representable as a moral order or a spiritual kingdom such as Leibnitz named, in words borrowed from St Augustine, a city of God.
The City of God and the Confessions are of unmatched importance in their several ways; and nothing of Augustine's was without influence.
Before this there had been complete harmony between Church and State; but afterwards came indifference and then disagreement between political and religious institutions, between the City of God and that of Caesar.