By Carol Symes, University of Illinois Urbana-Champaign
The formation of Judaism as a monotheistic religion was informed by contact with, as well as opposition to, the peoples among whom the Hebrews lived. The Jewish diaspora—beginning in the 6th century BCE and escalating again in the 1st and 2nd centuries CE—had established Jewish communities throughout Western Asia, North Africa, and the Aegean, creating a world that was already familiar with Jews, their beliefs, and their customs.

Enslavement and War
The Hebrews spread their religion through the Canaanites, Philistines, and other neighbors in Palestine and Egypt; but then, more devastatingly, under Neo-Assyrian domination of the northern kingdom of Israel; and then, the still more devastating conquest of the kingdom of Judah, and destruction of the Temple at Jerusalem by the Chaldeans under Nebuchadnezzar.

The ensuing enslavement and captivity of the Hebrews in Babylon after 586 BCE had the effect of strengthening the Hebrews’ collective identification with Yahweh. Religious leaders of this time, like the prophet Ezekiel, stressed that salvation could be found only through a shared commitment to the spiritual and ritual purity demanded by their God, and the denial of all other gods’ existence.
The Babylonian Captivity
These later events, which we call the Babylonian Captivity, were, therefore, key to forging a religion that transcended political power. Just as the prophets of this era taught that Yahweh existed outside His creation, so the people who worshiped him could exist outside a Hebrew kingdom.
In Babylon, the worship of Yahweh, therefore, became something different; it became Judaism, a religion that could survive even though there was neither a Hebrew ruling class nor a Hebrew homeland. Outside of Judah, Judaism flourished. This was an unparalleled development in the ancient world: the survival of a religion that had no political power to back it and no holy place to ground it, and whose adherents were scattered all over the known world.
Diasporic Jews

After 538 BCE when the Persian emperor Cyrus the Great conquered Babylon and allowed the Jews to return to their lands in the new Persian-governed province of Judea—even helping them to rebuild the Temple—many Jewish people remained and flourished in Babylon or elsewhere in Persia, while others had long since settled in Egypt.
As a result, the Judaism that had emerged in Babylon would be promulgated by a new generation of diasporic Jews like the prophet Ezra, who brought new methods of interpreting the Torah from Persia to Jerusalem; and Nehemiah, the Persian-appointed governor of Judea. After the conquests of Alexander the Great, these diasporic communities became integrated into a hybrid Hellenistic (“Greek-like”) world that encompassed Greece, Egypt, and the former Persian Empire.
This article comes directly from content in the video series The Medieval Legacy. Watch it now, on Wondrium.
Interconnectivity Helped the Spread of Judaism
Some Jews, indeed, resisted becoming too integrated; we know from The Books of the Maccabees that many cosmopolitan Jews embraced Greek customs to a degree that their fellow Jews deplored, and there were many factional rebellions against Hellenistic and then Roman governance by Jews who sought to establish an autonomous Jewish state.
But that did not occur, and so the Jews of Western Asia and the Mediterranean continued to live in a multicultural, pluralistic Roman empire. It was their very interconnectivity that had enabled the extensive travels of the Jewish Roman citizen-turned-Christian missionary, Paul of Tarsus.
Nor did this situation change very much after Constantine’s conversion and the adoption of Christianity as an imperial religion. Just as Jews had been exempted from ritual worship of the Roman emperor, even after their expulsion from Palestine in the 2nd century CE, so they were exempted from the prohibition of pagan religions at the end of the 4th century.
Like their forebears, the Romans of Byzantium may have regarded some Jews as a bit fanatical, and they were definitely squeamish about circumcision, but they respected their piety and ancient heritage.
Jews in the Islamic World
Again, this also did not change very much when many of these Jewish communities found themselves within the Islamicate world. There were clashes between Jews and Muslims, as between Muslims and Christians, but Islam did not call for their forced conversion and was officially tolerant of non-Muslims within Muslim domains.
Many Jews from Palestine had already been long settled in the territory of the Abbasid caliphate, which stretched modern-day Tunisia to Pakistan, and the Babylonian school of Rabbinic Judaism continued to flourish there. Indeed, it was under Islamic rule that Jews were allowed to return to Jerusalem.
Although, many historians have wisely warned against painting a too harmonious picture of religious coexistence in the Islamicate world. There was much more strife between the western Umayyad and eastern Abbasid caliphates, and between Sunni and Shiʽa factions within Islam, than between Muslims and Jews at large.
Jewish Diaspora Affected Economies
Finally, there is the basic fact of Jews’ integration into the thriving Mediterranean economy, which made Christians, Muslims, and Jews mutually interdependent. The archive of the Cairo Genizah documents the daily lives and commercial activities of that Jewish community, revealing their correspondence with Muslim and Christian merchants and bankers and the adoption of Arabic script for Hebrew transactions.
Jewish merchants began establish trading contacts, and even took up residence, in the Indian Ocean world. Historians have written extraordinarily illuminating studies that reveal the inner workings of Jewish networks and their close associations with the Christian mercantile empires of Genoa and Venice, as well as the many Muslim entrepôts of the Mediterranean littoral.
Common Questions about How the Jewish Diaspora Spread Hebrews All Over the World
The prophet Ezekial stressed that Hebrews should deny the existence of other gods and be committed to the spiritual purity demanded by their God to gain salvation. This led to an unprecedented development; since Yahweh existed outside His creation, so could Jewish people exist outside of their kingdom.
The Jews lived all around the areas which Alexander the Great conquered. But the Jews that accepted Hellenistic culture were frowned upon by those who wanted to keep their culture pure. In any case, they were free to practice their religion.
According to the Cairo Genizah, Jews were very active economically. They traded with Christians and Muslims and even adopted Arabic scripture for Hebrew transactions.