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.
Hasidic Judaism
Outside pressure was mounting in the early 20th century. In 1912, many Hasidic leaders partook in the creation of the Agudas Israel party, a political instrument intended to safeguard what was now named Orthodox Judaism even in the relatively traditional East; the more hard-line dynasties, mainly Galician and Hungarian, opposed the Aguda as too lenient. Mass immigration to America, urbanization, World War I and the subsequent Russian Civil War uprooted the "shtetl"s in which the local Jews lived for centuries and were the bedrock of Hasidism. In the new Soviet Union, civil equality first achieved and a harsh repression of religion caused a rapid secularization. Few remaining Hasidim, especially of Chabad, continued to practice underground for decades. In the new states of the Interbellum era, the process was only somewhat slower. On the eve of World War II, strictly observant Jews were estimated to constitute no more than a third of the total Jewish population in Poland, the world's most Orthodox country. While the Rebbes still had a vast base of support, it was aging and declining.