For the rest, so far as we can tell, the Arab tribes were not all alike concerned in these wars of conquest. The great camel-breeding tribes of the highlands of the interior, in particular, seem to have taken a much smaller share in them than the tribes of the northern districts of Yemen. It was a point of the utmost importance that the supreme command was almost throughout in the hands of men of the Koreish, who at that time proved themselves a race of born rulers. They led Islam from victory to victory, proving themselves good Moslems on the whole, but without renouncing their worldly wisdom. Above all we are constrained to admire the skill, caution, and boldness with which, from his headquarters at Medina, Omar directed the campaigns and the rudiments of reorganisation in conquered countries. This unpolished and rigidly orthodox man, who lived with the utmost Arab simplicity while an incalculable revenue was flowing into the treasury of the empire, proved one of the greatest and wisest of sovereigns. His injunction that the Arabs should acquire no landed property in the conquered countries, but should everywhere constitute a military caste in the pay of the state, was grandly conceived, but proved impracticable in the long run. Some of the Christian Arabs at first fought against the Moslem, but without any very great zeal. The majority of them soon exchanged a Christianity that had never gone very deep for the national religion. The great tribe of the Taghlib in the Mesopotamian desert was almost the only one in which Christianity retained its ascendency for any length of time, but it nevertheless fully participated in the fortunes of the Moslem empire, and even there the older faith gradually passed away, as it seems to have done among all Arabs of pure blood.