Throughout the history of Europe, Jews were the frequent target of vicious campaigns of vilification and persecution carried out by their Christian rulers and neighbors — all in the name of Christ. I can't help but be startled by the apparent incongruity between the ruthlessness of Christian anti-Jewish violence, and the fact that Christianity's roots were plunged so deeply in Jewish tradition.
Half the Christian Bible is, well, the Jewish Bible. Many of the most venerated figures in Christianity, from the Patriarchs to Jesus and the Apostles, were Jews — and so were the early Christians, inevitably. Christian discourse is littered with references to Jewish narratives, such as the Temple of Solomon or Noah's Ark. Christians knew that they worshiped the same God as Jews, unlike Muslims whom they misconstrued as pagans. Clearly Christians couldn't pretend they were foreign to Judaism, could they?
How did Christians involved in anti-Jewish violence rationalize their anti-Jewish behavior? Did they ever address that contradiction in any way?
Since no actual historians have responded and I think this is a really important question, here's my $0.02.
As I understand the scholarship, there are a few different theories as to the origin of Christian anti-Judaism. Some historians think Christians developed resentments towards Jews for attempting to convert them and non-Christian pagans to Judaism. Church fathers were constantly complaining about "Judaizers" and there is some evidence of prominent converts to Judaism in the first few centuries of Christianity.
Other historians think Christian anti-Judaism developed because of other conflicts unrelated to competitive evangelism. Jews had special exemptions from pagan ritual observance that Christians might have been envious of, and both groups may have vied for political or socioeconomic advantage within the Roman empire.
Yet other historians think that Christians developed anti-Jewish views for purely theological reasons. The Christians had to explain to themselves and each other why they had the best claim to inherit the Jewish scriptures, and the most convenient way for them to accomplish that was to assert the Jews themselves were disinherited of their covenant with God.
Of course, some historians will take a multi-factorial view, weighing each of these factors equally, or considering one factor to be more influential than others. I myself take the view that neither conflictual nor competitive theories of Christian anti-Judaism are likely the culprit, because Jews were not inclined towards active proselytization (even though they passively welcomed converts), and Christianity was too marginal of a movement compared to Judaism in the period in which Christian anti-Jewish polemics started appearing, so I'm not inclined to think Jews were too concerned with losing social status or political power to the nascent Jesus movement.
In my view, Christian anti-Judaism is best explained by the theological need for the church to claim exclusive interpretative authority of the Jewish scriptures, and to explain why the law of Moses no longer applied after Jesus's death and resurrection inaugurated the new covenant. I think this is best articulated by Miriam Taylor in her book Anti-Judaism and Early Christian Identity:
Why then did God prescribe this inadequate legislation? That the law was intended by God to be limited in time and place, formed an important element in the church's justification for the abandonment of the law. But the Christians had to account for God's purpose in proclaiming an inferior law which was destined to be surpassed. The answer to this key question was found, conveniently, in the moral degeneracy of the Jewish people. The Jews were a rebellious, hard-hearted and ungodly people, and the law was "given them as a means of mitigating some of these offensive qualities and endowing them with some consciousness of God" (Bokser 1973-4: 120-121). When Trypho inquires of Justin why the Christians don't observe the law, Justin levels the accusation back at him, claiming the prophets as witnesses to the obduracy of the Jews. They offend even against their own commandments (Justin, Dialogue 12). Irenaeus explains that God gave the law to the Jews on account of their stubbornness and insubordination (Irenaeus. Against Heresies 4.15.2; 4.16.4).
Of course, after this initial premise (that God gave the Jews the law as a temporary measure to mitigate their wickedness) was accepted, there were further developments along these lines--especially the accusation of deicide. These theological charges against the Jews eventually led to real persecution and oppression, higher taxes, pogroms, even an imperial decree under Justinian forbidding Jews from saying daily prayers.