Judges 2:14
And the anger of the LORD was hot against Israel, and he delivered them into the hands of spoilers that spoiled them, and he sold them into the hands of their enemies round about, so that they could not any longer stand before their enemies.
The anger burning against Israel and the handing over to plunderers was caused by idolatry, rebellion, and breaking covenant with God. The people departed from allegiance to Him and exalted what stood opposed to Him, choosing human ways instead of God's ways. As a result He left them vulnerable and exposed to spoilers who plundered them and to enemies round about, so that they were weakened and could no longer stand or withstand before their enemies.
That rejection of God's ways for human ways began a continuing downfall that did not stop until they became prey to the very nations whose practices they had chosen to follow. God's leaving the remaining nations in the land un-driven-out was both the consequence of that unfaithfulness and a test of whether Israel would still follow His way.
The oppression by enemies was discipline permitted by God, and when Israel cried to Him in distress He heard them and raised up a ruler to deliver them. Yet the people failed to recognize that their own sins had made them weak and vulnerable, and wrongly blamed their defeats on having no king with authority to command the armies.