Zoroastrianism was once one of the most prominent religions in the world. Once Iran was conquered by the Muslims, however, it began to decline. Now there are fewer than 200,000 Zoroastrians left, though it's growing more popular in Iraqi Kurdistan, so we may see them significantly expand in numbers.
Your challenge is to keep Zoroastrianism as a major religion. It doesn't necessarily have to be as powerful as it was before the rise of Islam, but there should be at least as many Zoroastrians as there are Jews.
Your challenge is to keep Zoroastrianism as a major religion. It doesn't necessarily have to be as powerful as it was before the rise of Islam, but there should be at least as many Zoroastrians as there are Jews.