In 1839 the Jews of Mashhad in Iran were forcibly converted to Islam by Shiʿi fanatics. Many of the converts, referred to as jadīd-i Islām (Pers.) or jadīd al-Islām (Ar.) by Muslims, and as “Mashhadis” by themselves and other Jews, continued to practice Judaism secretly. Several decades after the conversion, more than two-thirds of them moved to Khurasan and Afghanistan, where they returned to Judaism openly. Many settled in Herat, and in time, because they were better educated and wealthier, they assimilated the local Jews.

In the emirate of Bukhara, in contrast, the local Jews abs…