All human work is imperfect, because human nature is and this intrinsic imperfection of human affairs cannot be overcome by procrastination. - Arnold J. Toynbee

We may express the historical function of the Abbassid Caliphate as a 'reintegration' or 'resumption' of the Achaemenian Empire-the reintegration of a political structure which had been broken up by the impact of an external force, and the resumption of a phase of social life which had been interrupted by an alien intrusion.

Societies, not states, are 'the social atoms' with which students of history have to deal.

Now civilizations, I believe, come to birth and proceed to grow by successfully responding to successive challenges. They break down and go to pieces if and when a challenge confronts them which they fail to meet.