Princes or to other invaders, and they disappeared from History altogether. The little good that is ascribed to them was done by the natives whom they enslaved for the time being.
The Normans (when they were not absorbed by the natives, as they were in Normandy), returned to Scandinavia, and for nearly a thousand years they have exercised no influence on the world.
The Arabs founded empires which were managed by the subject races whose civilisation they stole and afterwards paraded as their own, as the Arabs did with the Persians. After a few generations they disappeared as the ruling race and since then they have played no role in History any more.
The Turks killed and robbed for centuries, only to leave the conquered countries virtually in the hands of the original natives: Greeks, Egyptians, and Syrians, and to have to obey the orders of the Germans, the next invaders, or to the British, as in Egypt.
The fact is that killing and robbing are against human nature, which, from time immemorial, has abhorred murder and theft. Not from any innate "affability", but because of all animals Man was the most intelligent, and most intent on self-preservation, which was best promoted by mutual help and aid. The Moral Laws, which serve as Standards of Civilisation, do not emanate from a mysterious, awful Being, as was formerly believed. Their origin has been traced to the human brain. In our time the truth of all this is so