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.)
Origins of Christianity
Several Jewish sects are known to have existed during the 1st century CE: the Essenes, Pharisees, Sadducees, Zealots, and Christians. After the destruction of the Second Temple in 70 CE, most of these sects vanished, but Christianity and the Pharisees survived, with Christianity gradually becoming a separate religion, and the Pharisees developing into Rabbinic Judaism, or simply Judaism. Rather than a sudden split, there was a slowly growing chasm between Christians and Jews in the 1st centuries, and it took centuries for a complete break to manifest.