The relationship of Christianity to Judaism has been one of the great themes in the history of Christianity. Christianity began as a movement within Judaism, and the question of whether non-Jewish converts to Christianity should also become Jews or conform to Jewish religious regulations concerned many early Christians, notably Saint Paul. Some early Christian sects argued that Christianity had replaced Judaism, which should be repudiated altogether. Mainstream Christianity’s adoption of the Hebrew Bible as the Old Testament, followed by the New Testament, implied continuity between Judaism and Christianity. For many believers, though, this also implied that Judaism had been replaced or superceded by Christianity and that Jews should therefore convert to the newer faith. Moreover, some interpretations of the Gospels implied that the Jewish people were responsible for the crucifixion of Christ.
Over the centuries, the question of the relationship between Judaism and Christianity has resulted in a long tradition of anti-Jewish ideas and persecution. As Europe became identified as Christendom from late antiquity through the early Middle Ages, Jews were left as the primary religious outsiders within a civilization that recognized itself as Christian. Christian churches and Christian theology often contributed to the persecution of the Jews.
During World War II, the Nazis in Germany attempted to exterminate the Jews of Europe, a program known as the Holocaust or the Shoah. Some of the Christian denominations in Germany actively cooperated with the Nazis; others passively accepted the Holocaust. The Roman Catholic Church is sometimes accused of failing to act to protect the Jews, and some thinkers argue that this alleged failure was rooted in theological tradition and culture. After the war, the experience of the Holocaust led many Christian thinkers to reconsider the relationship between Christianity and Judaism.