According to Renan, as far back as the second century, Bardesane had wondered that "If man is the creature of his surroundings and of circumstances, how is it that the same country is seen to produce human developments entirely different? If man is governed by the laws of race, how is it that a nation which has changed its religion, for example, become Christian, comes to be quite different from what it used to be?" [35] We have only to substitute the epithet Mahomedan for the epithet Christian to bring the question to the point. How, in fact, could such a radical change be effected, and to what degree of despair must the Zoroastrians have reached, to submit to the levelling laws of Islam? If we attempted to explain this we should have to go back to the history of the internal agitations and the policy of the Persian Court, and their study would draw us away too far. We have noticed only the chief events of its history, without stopping to gather any instruction from facts. Let it suffice to say that the same causes made the Arabs victorious over the Byzantine emperor and the Persian Shah-in-Shah, and that these causes were the weakness and exhaustion of the national dynasties in the presence of the vital elements of the conquerors. The people suffered from the carelessness of their kings; individual energy was powerless against the invasion of disciplined and fanatical tribes, commanded by generals like Omar and his officers. The Persian nation was singularly maltreated. [36] The national unity was broken. Each province accommodated itself in the best way it could to the regime imposed by circumstances and by the inclinations of local chiefs. From that time the boundaries of the ancient kingdom underwent changes from century to century. In the tenth century, Taher, governor of Khorassan, threw off the heavy yoke of the Caliphs of Bagdad, and established, in his province, the authority of the Taherides. After them came the Saffarides, the Samanides and all those foreign dynasties that divided the sovereignty amongst themselves, such as the Ghaznevides, the Seldjoukides, &c.; finally there came, with all its calamities, the torrent of invasions to which succeeded the reigns of the Sophis, and of those dynasties, cruel and grasping, which have succeeded each other on the throne of Persia without doing anything for the true welfare of the people. As we have seen, the followers of Zoroaster who would not accept the religion of Islam expatriated themselves. Those who could not abandon their country, and continued to cling to their old religion, had to resign themselves to frightful sufferings. These dwelt chiefly in Fars and Khorassan. European travellers who have visited Persia at different periods, have all been struck by their miserable and precarious condition, and have felt interested in their language, religion, and customs. We quote here some of them: