Challenge: Have a Medieval state convert to Judaism and liberate Jerusalem. Just throwing it out there: possibly the Khazars, but it in no way has to be them. The resulting Kingdom does not have to be an Empire, but should be strong enough to secure its own borders and to entice members of the Jewish diaspora to emigrate.
Added Discussion: How does Judaism develop if a ruler, claiming to be of the line of David, actually manages to retake the Holy Land from the Byzantines, the Caliphate or any successor state?
Added Discussion: How does Judaism develop if a ruler, claiming to be of the line of David, actually manages to retake the Holy Land from the Byzantines, the Caliphate or any successor state?