Judaism
Christianity was originally a sect of Second Temple Judaism, but the two religions diverged in the first century. The differences between Christianity and Judaism originally centered on whether Jesus was the Jewish Messiah but eventually became irreconcilable. Major differences between the two faiths include the nature of the Messiah, of atonement and sin, the status of God's commandments to Israel, and perhaps most significantly of the nature of God himself. Due to these differences, Judaism traditionally regards Christianity as Shituf or worship of the God of Israel which is not monotheistic. Christianity has traditionally regarded Judaism as obsolete with the invention of Christianity and Jews as a people replaced by the Church, though a Christian belief in dual-covenant theology emerged as a phenomenon following Christian reflection on how their theology influenced the Nazi Holocaust.
Jewish diaspora
During the Middle Ages, due to increasing geographical dispersion and re-settlement, Jews divided into distinct regional groups which today are generally addressed according to two primary geographical groupings: the Ashkenazi of Northern and Eastern Europe, and the Sephardic Jews of Iberia (Spain and Portugal), North Africa and the Middle East. These groups have parallel histories sharing many cultural similarities as well as a series of massacres, persecutions and expulsions, such as the expulsion from Spain in 1492, the expulsion from England in 1290, and the expulsion from Arab countries in 1948–1973. Although the two branches comprise many unique ethno-cultural practices and have links to their local host populations (such as Central Europeans for the Ashkenazim and Hispanics and Arabs for the Sephardim), their shared religion and ancestry, as well as their continuous communication and population transfers, has been responsible for a unified sense of cultural and religious Jewish identity between Sephardim and Ashkenazim from the late Roman period to the present.