I'm trying find out if the Christian and islamic world could have been balkanised during the medieval period so 1 sect or heresy can consolidate it's hold in one area and be surrounded by different ideologies around it. E.g. catholic Italy with its neighbours all run by different sects.
In OTL, the one major factor which contributed to the standardization of Christianity into one dominant orthodoxy is the Roman Empire. Then Islam imitated Christianity and developped its own orthodoxy.
In order to have a more varied picture, I believe it is necessary to have the Roman Empire disappear earlier and more thoroughly than IOTL. 2 possible PODs:
- Julian the Apostate is successful in reinstating Paganism alongside Christianity in the mid-IVth century. After his death, the ERE is plunged into a religiously motivated civil war that leads to its break-up.
- Constantinople is sacked at about the same time as Rome is (early Vth century) and as a result, both halves of the Empire are broken up into sucessor states.
In both TLs, we could have Manichee principalities, Jewish-Christian states, syncretic Pagan-Gnostic kingdoms, and so forth.