Judaism, famously non-proselytizing, was nevertheless adopted by the ruling dynasty of Yemen in the 5th century and the elite of the Khazars in the 8th and 9th. How did this happpen?

by pizza-flusher

I had known about the Khazars converting to Judaism from games and such for sometime, but recently learned about the Himyars in Yemen converting and the dynamics it added to their relation with Christian Ethiopia.

How/why did nations relatively distant from the Levant adopt Judaism as a religion?

Were the Jews always ambivalent/opposed to conversion or was this an explicit conversion campaign?

ylmz4

Rabbinical Judaism indeed isn't a proselytizing religion in a sense that it didn't actively spread itself and attempt to convert others like Islam and Christianity did, but conversions still happened, albeit on a smaller scale. In Khazars' case upper nobility most likely converted to Judaism in an attempt to avoid the hatchet fight that were the wars between the Byzantine Empire and the Abbasids.

If they had accepted Christianity, they would inevitably be subordinates to the Patriarch of Constantinople, and if they had accepted Islam, they would have been subordinates to the Caliph of Baghdad, as these two cities were closest centers of these religions. However, as nomadic steppe religions were becoming too primitive to support further growth and articulation of state structures, there was an incentive to adopt one of the universal religious systems of sedentary civilizations, as many other Eurasian states in the mid 8th century did. In this case this might've been further helped by an influx of Jewish refugees fleeing Byzantine and islamic persecution, so their lobby might have influenced the Khazar rulers to convert.

What needs to be understood here however is that historical sources on Khazars are rather thin, and what we do have left is sometimes of disputable authenticity like the controversial correspondence between Hasdai ibn Shaprut and Khagan Joseph. Similarly, we only have evidence that suggests the upper class converted. Islam, Christianity, and pagan religions were most likely still widespread among the lower class. All of this supports the notion that the conversion was purely political. The reason why the Khazars were seen as a heathen tribe by Judas Halevi is precisely because they were not sincere in their faith, and the elite of the khaganate had converted primarily for material reasons. Their deeds fell short of what God had commanded of them were they truly Jewish, which is why the rabbinical process to determine whether or not a supposed convert has a jewish soul is so thorough. This I guess partly answers your last question as well, although the historical sources are far too scarce to reconstruct what the Jewish community as a whole thought of that entire ordeal.