Zoroastrianism in China during the Tang dynasty? I have never read about that, perhaps I am mistaken but as far as I know there were no large communities of Zoroastrians in the Tang dynasty at that time.
During the Great Anti-Buddhist Persecution, monasteries (or so they were called) of Christians and Zoroastrians were lumped in with Buddhists and forced to integrate back into the population. Compared to the Buddhists this was not so many people, but it probably amounted to a fairly large number of people in an absolute sense. Zoroastrianism existing in the Tang dynasty should maybe not be so surprising given Persia's position on trade routes between China and the Mediterranean, and how religions tend to spread along trade routes. It would really be more surprising if there
weren't any adherents of the ~1000+ year old religion from
right there in China.
Again, it is easy to just say, well a new dynasty rises and for some reason throws away 100s of years of tradition over night. I personally see it as at least taking time.
But there were earlier dynasties that had different policies. There's nothing saying that you couldn't make changes much earlier than the Sassanids, with Zoroaster himself if necessary. As I keep saying, the Sassanids only defined Sassanid Zoroastrianism, not Zoroastrianism as a whole.
Zoroastrianism again is not a religion like the Abrahamics, it in its social application is like Hinduism (or religions making up), the religion of a ethno-region rather than the whole world.
Interestingly, Hinduism has actually been quite successful in spreading, historically, to Southeast Asia. And of course the Hindu-derived Buddhism quite successfully spread to China and other regions of East Asia. Zoroastrianism itself was closely related to Hinduism (also being derived from the proto-Indo-Persian religion) and had some success in spreading into the steppe, so it's quite plausible that a more missionary branch arises.
While again I understand your point, but why exactly would Bactrian Zoroastrians reform and run off to China and begin to convert the masses whenever there was no effort beforehand and that it is not supported by other Zoroastrians?
For the same reason that Bactrian Buddhists ran off to China and began to convert the masses? In any case you're missing my point, which is that the religion itself had a diversity of practices and beliefs (as all religions do), and the practices and beliefs of Kartir, while inapt for converting China, are not the totality of nor define Zoroastrianism.
How is Kartir irrelevant to Zoroastrians in Bactria?
I didn't say he was irrelevant to Zoroastrians in Bactria specifically, I said what he thought was irrelevant as far as analyzing the religion for the purpose of the discussion is concerned except inasmuch as it impacts the conversion of Chinese. Kartir does not define Zoroastrianism, he defines Kartir's Zoroastrianism, which is no one else's Zoroastrianism. It is true that he had the ability to make other people emulate his Zoroastrianism much more closely than usual, but this should not be mistaken for defining the religion.
In the event, the point is that too much shouldn't be read into his beliefs about Zoroastrianism. While
his version of Zoroastrianism is inapt for transmission into China, and the Sassanids little invested in it, that does not mean that
the religion is identically inapt, nor that other people have other beliefs that might be more apt for transmission into China, nor that other practices and beliefs might be adopted that would be more attractive to the Chinese.
That is like saying the Caliph is a nobody to Sunni Muslims in India during the 1100s.
The Caliph
was a nobody to Indian Muslims in the 1100s, or, rather, irrelevant (just as I was saying Kartir was). He had no practical ability to enforce any decisions he might make about what practices were orthodox and which were not, meaning that practices which did not conform to his conception of orthodoxy had the ability to thrive--as, indeed, they did, at that time and later (as with, e.g., Sikhism or Sufism). There were many such regions of the Islamic world where the Caliph's writ was merely moral in force, and where subsequently many non-Caliphal religious practices ended up growing. The fact that he had a certain
moral influence shouldn't be taken indicate he had any
practical influence.
Also ,I might be ignorant, but I thought it was during the Ming that Christians were persecuted in China and were thus removed from the region.
Christianity has flourished and been suppressed in China several times.