Zoroastrianism had been practiced since the proclamations of Zoroaster (1500-500 BCE), but it thrived with 40-50 million followers as the official religion of Iran during the Sassanid Empire (224-651 CE). However, the Sassanid empire’s fall to Arab Muslims in 651 CE changed the face of Zoroastrianism for good. Consolidation of rule under the Arab Caliphate eventually resulted in the massacre of numerous Zoroastrians, and the escape of 7 boatloads of believers to the west coast of India. Iranian scholarship, documents and other writings were destroyed, and the Iranian region saw conversions to Islam over the next 5 centuries.
What was left of Zoroastrianism was initially found in India, where descendants (Parsis) settled and built Bombay into the Zoroastrian capital of the world in 936 CE. The subsequent diaspora of Zoroastrians around the world (North America, Australia, Persian Gulf nations) also meant that there was no single place or homeland for Zoroastrians to settle or call home, and no solid cultural heritage to cling on to.
The Beginning of the End
Some argue that the very tenets of the world’s oldest monotheistic religion is one of the main reasons for its demise. Free will under Zoroastrianism determines that no one can be forced into believing in the religion or into practicing it. By entrusting choice and responsibility in the hands of each individual to make positive choices, it was meant to help God annihilate evil and return the universe to goodness. However, this free will also means that people could convert out of, not practice, or no longer subscribe to the beliefs of the faith - as and when they please.
The faith's belief in gender equality is another reason for its own decline. In early Iranian society, women were regarded as "men’s partners in the common struggle against evil”. Gender parity has brought about more career-driven women who in comteporary times de-prioritize having families and partaking heavily in the religion. Therefore, this has resulted in lower propagation of Zoroastrian children and of the religion. If there is no constant reminder or obligation to be faithful, or no common struggle (instead different priorities), keeping people together under a singular faith is difficult.
Disfavour of Proselytising and Intermarriage
Despite the fact that Avestan scriptures state that individuals are meant to help enlighten one another and eventually bring everyone under Mazda's religion to abandon evil, many Zoroastrians in North America and India (especially) avoid converts because it is socially adverse to their community. This in part is because such Zoroastrians are very wealthy and established, and have built very successful lives for themselves as a community. Furthermore, as descendants they continue to hold on to the Zoroastrian glory from pre-Islamic Iran, many - especially the Parsis - are against accepting the “admixture of racial blood that the low class of aliens introduced into the community”. Although the issue seems to be more divisive in North America than in India (more stringent) the existence of such piousness has led to their very decline.
Similarly, the issue of intermarriage is seen as a threat to the survival of the community. The reason for this lies not in the dilution of the faith’s purity or piousness, but more as a safety-response: Zoroastrians (especially women) who intermarry seem to eventually isolate themselves, and their children from the religion and the Zoroastrian community. However, the issue seems to lie in the fact that intermarried women need to be more responsible for including her family into the religion, and making this clear from the beginning of her relationship with her partner. Preventing intermarriage doesn’t only create resentment and a divide within the community, but also means that the community is losing the opportunity to gain potential followers (children, as well as husbands, if converts are allowed).
In cities and civilised communities today, it is not conducive to practice certain Zoroastrian rituals . For instance, their death ritual involves disposing the body to scavengers, their purification ritual involves drinking consecrated bull urine (Nirangdin), and their menstruating women are kept away from people, work and public spaces. While their death ritual is still performed in Mumbai today, it is generally more difficult to partake in such rituals in other countries especially since the number of priests able to conduct these rituals are running low.
In such a dire state where the number of descendants are low, converts are not allowed, intermarriages are feared and frowned upon, and where women (and men) have different priorities, it would be naive to think that the religion can survive in numbers.
However, I propose another way to look at things.
Zoroastrianism predates Islam and Christianity, and some argue that the latter two have been influenced by Zoroastrianism (namely one God, Good/Evil dualism in cosmic and mental nature, and a final judgment day). Today, many more people don’t subscribe to an organised religion or are "religiously unaffiliated”, but it doesn’t necessarily mean that they don’t follow a rough moral or ethical framework to guide their thoughts and actions. While the traditional rituals may be dying, the very tenets of Zoroastrianism and the value system it embraces is perhaps something many spiritual aspirants are already living by: “Good thoughts, good words, good deeds”.
Arguably, in its essence, Zoroastrianism is a universal and humanitarian religion. So, perhaps we could look at it from the perspective that it’s not dying - but that instead, its virtues have already been so deeply interwoven in our ethics through the world around us, that it could be everlasting in the human conscience.