TSK · 2 Chronicles 12:8

instead in hunger, thirst, nakedness, and poverty you will serve your enemies whom the LORD will send against you. They will place an iron yoke on your neck until they have destroyed you.

He left those nations simply because he wanted to teach the subsequent generations of Israelites, who had not experienced the earlier battles, how to conduct holy war.

Their enemies oppressed them; they were subject to their authority.

Correct us, LORD, but only in due measure. Do not punish us in anger or you will reduce us to nothing.