Will Durant on empire

... it is the fatality of empire to breed repeated war.  For the conquered must be periodically reconquered, and the conquerors must keep the arts and habits of camp and battlefield; and at any moment the kaleidoscope of change may throw up a new empire to challenge the old.  In such a situation wars must be invented if they do not arise of their own accord; each generation must be inured to the rigors of campaigns, and taught by practice the sweet decorum of dying for one's country.

~ Will Durant, Our Oriental Heritage, Page 355