Complex sentence: Leipzig (1882) It is thought that during the 17th century, like in the whole surrounding region, its inhabitants were converted from "Paulicianism" to Islam and since then they were called "Pomaks" (Muslim Bulgarians).
Split into simpler sentences: Leipzig (1882) As in the whole surrounding region, an islamization process has taken place during the 17th century. The population converted from "Paulicianism" to Islam and started to be known as "Pomaks" (Muslim Bulgarians).