Louis Halle, The Cold War as History (1967):
... real power is always something far greater than military power alone. A balance of power is not a balance of military power alone: it is, rather, a balance in which military power is one element. Even in its crudest aspect, power represents a subtle and intimate combination of force and consent. No stable government has ever existed, and no empire has ever become established, except with an immensely preponderant measure of consent on the part of those who were its subjects. That consent may be a half-grudging consent; it may be a consent based in part on awe of superior force; it may represent love, or respect, or fear, or a combination of the three. Consent, in any case, is the essential ingredient in stable power--more so than physical force, of which the most efficient and economical use is to increase consent.
By using physical force in such a way as alienates consent one constantly increases the requirements of physical force to replace the consent that has been alienated. A vicious spiral develops that, continued, ends in the collapse of power.