There are myriad reasons for how the Jews became scattered across Christian Europe. Generally speaking, however, Christian rulers often invited Jews to settle within their realms, and just as often expelled them, forcing the Jews to find other homes elsewhere on the continent, and so on. The aim of this reply is to explore this pattern in much more depth. Note that while this pattern intensified in Europe during the High Middle Ages, it did not end in the Middle Ages. Even after the conclusion of the Middle Ages, Jewish communities became even more scattered throughout Europe.

Dispersal

To show the necessary context for how the Jews became dispersed, let me answer why they became so dispersed in the first place.

Shortly before 66 CE, millions of Jews lived all over the eastern Mediterranean seaboard. The largest Jewish community lived in Judea, then under Roman occupation. Another large Jewish community lived in Egypt, also under Roman occupation. The city of Alexandria specifically had a very large and vibrant Jewish community. Other substantial Jewish communities lived in Mesopotamia, Syria, Asia Minor, Southern Europe and the Balkans. In fact, several hundred thousand Jews may have lived in the Balkans at this time.^(1)

The Jews never completely accepted the Roman occupation of their country. Widespread financial corruption and growing Roman interference in religious matters stoked massive flames of resentment and anger. Growing tensions soon exploded into open war:

The revolt began in 66 CE in the town of Caesarea, apparently provoked by the failure of the Roman garrison stationed there to intercede to stop Greeks from sacrificing birds in front of a local synagogue. During the initial stages of the war, the rebels defeated the Romans.^(2)

A year later, however, Emperor Nero appointed General Vespasian as commander of the Roman forces in Judea. Vespasian captured important Jewish strongholds in the Galilee, thereby rendering the positions of the remaining rebels untenable. Political instability in the wider Roman Empire, however, provoked Vespasian to abandon Judea and return to Rome, where in 69 CE he was proclaimed the new Roman Emperor. To finish what he had started in Judea, Emperor Vespasian sent his son Titus to besiege and capture Jerusalem. In 70 CE, Titus’ forces broke through the rebel defenses in Jerusalem, destroying both the city and the Second Temple.^(3)

The destruction of the Second Temple and the legal constraints that Roman authorities placed on Jews enraged Jews everywhere. In 115 CE, Diasporic Jewish communities all across the eastern Mediterranean seaboard rose up in open rebellion against Rome, fighting the Roman legions sent to crush them. This came to be known as the Kitos War.

Then Emperor Hadrian ascended to power. Under his rule, the Roman authorities issued a series of edicts that the Jews considered sacrilegious; one of the edicts, for example, banned circumcision, a central tenet of Judaism. To add fuel to a massive inferno, the Emperor decided to construct a new city in Jerusalem in which a temple to Jupiter would be erected, thereby eroding the physical foundations of the ancient Jewish faith. In 132 CE, the Judean Jews under the leadership of Simon bar Kokhba initiated yet another war to retake their homeland.^(4)

The scale of and the vindictiveness with which this war was fought cannot be overstated. In the first phase of the war, the Jews decisively defeated the Roman forces arrayed against them, inflicting catastrophic losses, and likely annihilated an entire Roman legion.^(5, 6) To crush the uprising, Hadrian deployed a gargantuan force of twelve legions against the Jewish rebels.^(7) At the time, all Roman forces everywhere added up to around thirty legions,^(8) so Hadrian’s force comprised over one-third of the entire Roman army.

Even with this massive force deployment, it still took the Romans another three and a half years to exterminate Bar Kokhba’s rebels,^(9) and they still sustained shockingly high casualties—the Jews possibly annihilated another whole legion.^(10) At the conclusion of the war, Hadrian—in an unprecedented move—completely changed the name of Judea to Syria Palestina. The historian Werner Eck explains the significance of this name-change:

Not that revolts were not frequent in other provinces as well: the Germani in Germania, the Pannonii in Pannonia, and the Brittones in Britannia all revolted against Rome at one time or another. Yet none of these provinces lost its original name derived from the name of its people. But Judaea, derived from Iudaei, ceased to exist for the Roman government after the Bar Kokhba revolt. It was not because the Jewish population was much reduced as a result of losses suffered during the war that the name of the province was changed; the same was true, for example, of Pannonia, and yet the old name was kept. The change of name was part of the punishment inflicted on the Jews; they were punished with the loss of a name. This is the clear message of this exceptional measure, the one and only example of such a measure in the history of the Empire.^(11)

The Romans throughly destroyed the Jewish community in Judea. Without their homeland, the surviving Jewish communities became desperately scattered all over the Empire. Shortly after the Jewish-Roman Wars, the Jewish community in the Galilee became the largest and most important Jewish outpost. Later in the 3rd Century, the declining economy of Syria Palestina caused many Jews to immigrate to Mesopotamia, thereby leaving a scant presence in what was formerly the Land of Israel.^(12) What followed was a massive Jewish demographic decline throughout the Middle East and Europe that lasted until the 7th Century.^(13) Due to Roman and later Christian persecution, Jewish communities all over the eastern Mediterranean seaboard—including the aforementioned Balkan community, and other Jewish communities in Europe—dwindled into irrelevance.

(Continued below)