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.
Orthodox Judaism
Orthodox Judaism is not a centralized denomination. Relations between its different subgroups are sometimes strained, and the exact limits of Orthodoxy are subject to intense debate. Very roughly, it may be divided between Ultra-Orthodox or "Haredi", which is more conservative and reclusive, and Modern Orthodox Judaism which is relatively open to outer society. Each of those is itself formed of independent streams. They are almost uniformly exclusionist, regarding Orthodoxy as the only authentic form of Judaism and rejecting all competing non-Orthodox philosophies as illegitimate. While adhering to traditional beliefs, the movement is a modern phenomenon. It arose as a result of the breakdown of the autonomous Jewish community since the 18th century, and was much shaped by a conscious struggle against the pressures of secularization and rival alternatives. The strictly observant and theologically aware Orthodox are a definite minority among all Jews, but there are also numerous semi- and non-practicing persons who are officially affiliated or personally identifying with the movement. In total, Orthodox Judaism is the largest Jewish religious group, estimated to have over 2 million practicing adherents and at least an equal number of nominal members or self-identifying supporters.