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Zoroastrianism /?z?ro??æstri?n?z?m/ (or Mazdaism) is a religion and philosophy based on the teachings of prophet Zoroaster (also known as Zarathustra, in Avestan) and was formerly among the world's largest religions.[1] It was probably founded some time before the 6th century BCE in Greater Iran.

In Zoroastrianism, the Creator Ahura Mazda is all good, and no evil originates from him. Thus, in Zoroastrianism good and evil have distinct sources, with evil (druj) trying to destroy the creation of Mazda (asha), and good trying to sustain it. Mazda is not immanent in the world, and his creation is represented by the Amesha Spentas and the host of other Yazatas, through whom the works of God are evident to humanity, and through whom worship of Mazda is ultimately directed. The most important texts of the religion are those of the Avesta, of which a significant portion has been lost, and mostly only the liturgies of which have survived. The lost portions are known of only through references and brief quotations in the later works, primarily from the 9th to 11th centuries.

In some form, it served as the national or state religion of a significant portion of the Iranian people for many centuries. The religion first dwindled when the Achaemenid Empire was invaded by Alexander III of Macedon, after which it collapsed and disintegrated[2] and it was further gradually marginalized by Islam from the 7th century onwards with the decline of the Sassanid Empire.[3] The political power of the pre-Islamic Iranian dynasties lent Zoroastrianism immense prestige in ancient times, and some of its leading doctrines were adopted by other religious systems. It has no major theological divisions (the only significant schism is based on calendar differences), but it is not uniform. Modern-era influences have a significant impact on individual and local beliefs, practices, values and vocabulary, sometimes complementing tradition and enriching it, but sometimes also displacing tradition entirely.

... according to Wikipedia