Origins of Judaism
For centuries, the traditional understanding has been that Judaism came before Christianity and that Christianity separated from Judaism some time after the destruction of the Second Temple in 70 CE. Starting in the latter half of the 20th century, some scholars have begun to argue that the historical picture is quite a bit more complicated than that. In the 1st century, many Jewish sects existed in competition with each other, see Second Temple Judaism. The sects which eventually became Rabbinic Judaism and Early Christianity were but two of these. Some scholars have begun to propose a model which envisions a twin birth of Christianity and Judaism rather than a separation of the former from the latter. For example, Robert Goldenberg (2002) asserts that it is increasingly accepted among scholars that "at the end of the 1st century CE there were not yet two separate religions called "Judaism" and "Christianity"".
Daniel Boyarin (2002) proposes a revised understanding of the interactions between nascent Christianity and nascent Rabbinical Judaism in Late Antiquity which views the two religions as intensely and complexly intertwined throughout this period.
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.