At first sight it seems strange that the terrible warriors who, under Set or Saites, so easily reduced Egypt to subjection, and then still further weakened the population by massacre and oppression, should have been got rid of, after two centuries or two centuries and a half, with such comparative ease.  But the rapid deterioration of conquering races under certain circumstances is a fact familiar to the historian.  Elamites, Babylonians, Assyrians, Medes, Persians, Greeks, rapidly succeeded each other as the dominant power in Western Asia, each race growing weaker and becoming exhausted, after a longer or a shorter interval, through nearly the same causes.  Nor are the reasons for the deterioration far to seek.  Each race when it sets out upon its career of conquest is active, energetic, inured to warlike habits, simple in its manners, or at any rate simpler than those which it conquers, and, comparatively speaking, poor.  It is urged on by the desire of bettering its condition.  If it meets with a considerable resistance, if the conquest occupies a long space, and the conquered are with difficulty held under, rebelling from time to time, and making frantic efforts to throw off the yoke which galls and frets them, then the warlike habits of the conquerors are kept up, and their dominion may continue for several centuries.  Or, if the nation is very energetic and unresting, not content with its earlier conquests, or willing to rest upon its oars, but continually seeking out fresh enemies upon its borders, and regarding war as the normal state of its existence, then the centuries may be prolonged into millennia, and it may be long indeed before any tendency to decline shows itself; but, ordinarily, there is no very prolonged resistance on the one side, and no very constant and unresting energy on the other.  A poor and hardy people, having swooped down upon one that is softer and more civilized, easily carries all before it, acquires the wealth and luxury which it desires, and being content with them, seeks for nothing further, but assimilates itself by degrees to the character and condition of the people whom it has conquered.  A standing army, disposed in camps and garrisons, may be kept up; but if there is a cessation of actual war even for a generation, the severity of military discipline will become relaxed, the use of arms will grow unfamiliar, the physical type will decline, the belligerent spirit will die away, and the conquerors of a century ago will have lost all the qualities which secured them success when they made their attack, and have sunk to the level of their subjects.  When this point is reached, thoughts of rebellion are apt to arise in the hearts of these latter; the old terror which made the conqueror appear irresistible is gone, and is perhaps succeeded by contempt—­the subjects feel that they have at least the advantage of numbers on their side; they have also probably been leading harder and more bracing lives; they see that, man for man, they are physically stronger than their conquerors; and at last they rebel, and are successful.