Role of Persian empire
Role of Persian Empire in the Growth of the World’s Religious Thoughts
The great change that the ancient world underwent, was its unification from Sind to Mediterranean region under the leadership of the Acheamenids. This unification that brought about peace all over the civilized world after destructive actions of Assyrians and Babylonians encouraged a sort of human identity and a sort of thought that was superior than ethnic identity; in fact the great Achaemenid king by the grace of the mono god realized the ideal unification of a world that has ethnic, cultural and geographical diversity. In this universal community, anyone with any national identity and with any religion and traditional background was respected and could have an influential role in its development.
As a result of security, human transportation throughout the Achaemenid world was facilitated and a lot of people from merchants and technicians to the ones who seek wisdom and knowledge travelled all over the civilized world so that the communication of different people with each other was made possible. This lead to the exchange of thoughts from different schools; For example, it has been suggested that Taoists of the late Han period borrowed their term for "the highest heaven", ta-lo, from the Iranian garo dmana, the "house of praise", the highest of the four heavens, associated with Ahura Mazda who is referred to in parts of the Avesta as Dadhvah. Also Greece at the end of the Persian period had developed a lot compared to its past; before this period, the Greek thought was based on primitive mythologies and several godheads that had lives and deaths like humans, but during this period its thought gradually changed from physical speculations to metaphysical ideas that could be accepted by the whole world. In fact the growth of Greek civilization and the arise of philosophy that we can trace its roots in Iranian beliefs in this period as Mary Boyce in her masterpiece, “history of Zoroastrianism” described, caused the magnificence of Greek school of thoughts.
Although Achemenid great kings because of the their way of thinking and also for the stability of their hegemony tolerated different religions and do not force others to convert to their religion, effective dominancy of Iranians brought about acquaintance of peoples of different countries to Iranian thoughts; this school of thought that was total different from that of Semitic thoughts, was a universal school that with the support of a universal government could be well influential.
All these social and human evolutions generalized some religious beliefs and founded a basis for universal religions. These novel principles were: (1) universal monotheism, God is universal and is not tribal, he created the universe and we all are equal in his view; (2) good and evil principles, that the symbol of goodness is God and the symbol of devil is Ahriman or Satan or whatever it was called in different nations; (3) eschatological rewarding & punishment based on our deeds in our life.
The open-mindedness of Iranian governors prevented the conversion of other people to Iranian religion; in fact although Zoroastrianism has a universal basis, it stayed an Iranian religion, since Iranians were not to force others and were not to export it! Besides, other people were influenced by Iranian beliefs. Universality and the monotheism that can be observed in different religions were attained after the experience of Achaemenid unification and under the influence of Iranian beliefs. It was during and after the Persian empire that tribal characteristics of Judaism faded and this lead to Christianity and it was after this glorious period that Buddhism obtained its international characteristic and was spread from India to far east; whereas before this period, religions were tribal and polytheism was spread. The rise of universal Persian empire and the attitude of its great kings to unify the civilize world and its influence on Judaism and Buddhism is the greatest historical impact of Iran on the human life. Great religions of the world have their root to this period. Christianity & Islam are continuances of Judaism and the thing that ascended and perfected Judaism was Iranian influence. Herzfeld in his Archeological history of Iran (p 56) says: “Zoroastrianism, Jewish beliefs and Buddhism are the evidence of unique development of human thought as a result of the Achaemenid peace”.
 Homer H. Dubs, "Taoism," in H.F. MacNair, ed., Philosophy and Religion, Berkeley and Los Angeles: University of California Press, 1946, pp. 286-7
 Eschatological ideas about rewarding & punishment was totally Iranian beliefs; any religion (i.e. later Judaism, Christianity and Islam) that has this kind of ideas loaned them from Iranian beliefs. However It should be pointed out that Indian beliefs of reincarnation and also the idea of Nirvana were of pure Indian beliefs. Generally speaking, the novel ideas about the other life were of Aryan people. Zoroaster and Iranians declared the idea of resurrection and rewarding & punishment and Buddha and Indians declared the idea of reincarnation & Nirvana.