Further Jewish intermingling with other cultures and their thought.
The captivity in Babylon have brought the captive Jews face to face with another more powerful culture and the mythical stories of the Babylonians.
And, then came the defeat of the Babylonians by the Persians (Iranians). This was a powerful influence, as the Jewish writers makes Yahwehsay that Cyrus was his shepherd. (Isaiah 44:28). And that Cyrus was Yahweh's 'Christ.' It would also have brought them into contact with proto-Zoroastrianism and the idea of dualism.