History of ancient Israel and Judah
Without a powerful king, the Temple became more powerful, and priests became the dominant authority.  However, the Second Temple had been constructed under a foreign power, and there were lingering questions about its legitimacy.  This provided the condition for various sects to develop within Judaism over the coming centuries, each of which claimed to represent "Judaism". Most of these typically discouraged social intercourse, especially marriage, with members of other sects.