ujm – Is anyone here familiar with the migration trajectory of Ashkenazim, Sephardim, etc.? As in, which came from Eretz Yisroel, which from Bavel, etc. And where the separation formed between Ashkenazim, Sephardim, and others.
The Jewish communities of Iraq and Iran most definitely came from Bavel. The Jews of the island of Djerba, in Tunisia, claim descent from two Mishmaros of Kohanim who were exiled there from Eretz Yisroel at the time of Churban Bayis Sheini. Seeing as Djerba was geographically isolated from the Goyish urban centers, did not get chased repeatedly from place to place like most other kehillos in Golus, and was a major ???? ???? for centuries, they preserved their Mesorah unusually well. The Yemenite Jews were there since Churban Bayis Rishon. Interestingly, certain Teimani minhagim are similar to old Ashkenazi minhagim (the square Kesher Shel Rosh being one example.) Since the last time our ancestors met was probably at the Aliyah LaRegel in the First Beis Hamikdash, that shows an amazing continuity of Mesorah. The first Jews in Western Europe, including both Ashkenaz and Sepharad, were probably those exiled there by the Romans. Afterwards it’s possible some came there from Bavel too, via the Byzantine Empire and Italy.
The emergence of Ashkenazim and Sephardim as distinct groups is generally considered to have started at the end of the Tekufah of the Geonim. Until then, all major Halachic shailos that couldn’t be resolved locally would be sent to the great Yeshivos at Pumbedisa and Sura. Many travelled all the way to Bavel to learn there, like Rabbeinu Gershom did. When Moslem persecution in Bavel, and increasing danger traveling, made that system end, the local Yeshivos took over. In Spain the Yeshivos followed the teachings and Mesorah of Rabbeinu Chananel and the Rif, and in Germany that of Rabbeinu Gershom and his Talmidim (who in turn were the Rebbeim of Rashi). There was a Torah presence beforehand in both places, but everyone was subordinate to the Geonim of Bavel, who had a direct living Mesorah from the Amoraim.