Judaism
Around the 1st century CE, there were several small Jewish sects: the Pharisees, Sadducees, Zealots, Essenes, and Christians. After the destruction of the Second Temple in 70 CE, these sects vanished. Christianity survived, but by breaking with Judaism and becoming a separate religion; the Pharisees survived but in the form of Rabbinic Judaism (today, known simply as "Judaism"). The Sadducees rejected the divine inspiration of the Prophets and the Writings, relying only on the Torah as divinely inspired. Consequently, a number of other core tenets of the Pharisees' belief system (which became the basis for modern Judaism), were also dismissed by the Sadducees. (The Samaritans practiced a similar religion, which is traditionally considered separate from Judaism.)
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.