Zoroastrianism
In order to understand properly the religion of Zoroaster, it is necessary to know something of the state of religion in Iran before the great Teacher appeared. New faiths have to be grafted upon old ones. All great teachers have built upon the past traditions of the race. They have to come to lead. They alter and adapt the Eternal Ancient Wisdom to the peculiar needs of that race, to the particular Message which that race is destined to leave for humanity. So also the Lord Zoroaster found a certain mass of tradition in Iran and the Message He gave to this branch of the human race was based upon what they had inherited from a dim and distant past.
The Aryans (using the word in its narrower sense, as comprising the two peoples, the Indians and the Afghans, who called themselves by that proud name) had lived together for long ages in one land, had spoken one tongue and had followed one religion. Where that ancient Motherland of the Aryans was, we have now no means of determining, but it seems to have been a region far to the North, which, according to the Aryans tradition, was overwhelmed and destroyed by ice and snow. At a later period the two main stocks of these people migrated southwards, still keeping together, and after many generations of wandering, ultimately arrived in the neighborhood of the high mountainous region of Pamir table-land today. They spread around from that region into the lower fertile and salubrious valleys of the south, west and east. The lands called by us Afghanistan and Bactria were the regions where the Aryans had long carried on their activities.