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.
Reform Judaism
The various regional branches sharing these beliefs, including the American Union for Reform Judaism (URJ), the Movement for Reform Judaism (MRJ) and Liberal Judaism in Britain, and the Israel Movement for Reform and Progressive Judaism, are all united within the international World Union for Progressive Judaism. Founded in 1926, the WUPJ estimates it represents at least 1.8 million people in 50 countries: close to a million registered adult congregants as well as numerous unaffiliated individuals who identify with it.