6th Century BC (During the Babylonian Exile)
The Israelites were in exile in Babylon, having been removed from their homeland due to their disobedience to God. The culture was heavily influenced by Babylonian polytheism and idolatry.
Babylon was the dominant empire, having conquered Jerusalem and taken many Israelites into captivity. The Babylonian king at the time was Nebuchadnezzar II.
The prophecy is directed towards the 'mountains of Israel,' symbolizing the high places where idolatry was practiced. The Israelites were physically in Babylon, but the message concerns their homeland.
Idolatry was rampant among the Israelites, despite their covenant with Yahweh. The high places were often used for worshiping foreign gods, which was against the commandments given to Israel.
Ezekiel