Perhaps the most quoted passage in The Parable of the Tribes explained how civilization would necessarily be compelled to evolve in directions shaped by the demands of power:
“Imagine a group of tribes living within reach of one another. If all choose the way of peace, then all may live in peace. But what if all but one choose peace, and that one is ambitious for expansion and conquest? What can happen to the others when confronted by an ambitious and potent neighbor? Perhaps one tribe is attacked and defeated, its people destroyed and its lands seized for the use of the victors. Another is defeated, but this one is not exterminated; rather, it is subjugated and transformed to serve the conqueror. A third seeking to avoid such disaster flees from the area into some inaccessible (and undesirable) place, and its former homeland becomes part of the growing empire of the power-seeking tribe. Let us suppose that others observing these developments decide to defend themselves in order to preserve themselves and their autonomy. But the irony is that successful defense against a power-maximizing aggressor requires a society to become more like the society that threatens it. Power can be stopped only by power, and if the threatening society has discovered ways to magnify its power through innovations in organization or technology (or whatever), the defensive society will have to transform itself into something more like its foe in order to resist the external force.
“I have just outlined four possible outcomes for the threatened tribes: destruction, absorption and transformation, withdrawal, and imitation. In every one of those outcomes the ways of power are spread throughout the system. This is the parable of the tribes.”)
[These four outcomes are discussed and illustrated in the published book (The Parable of the Tribes) in a section – pp. 34-42 — titled “Heads I Win, Tails You Lose: The Nonalternatives of the Parable of the Tribes.”]
The social evolutionary force identified by “the parable of the tribes” can be described as an inevitable selection for power.