Judges 2:21 (KJV)

And it came to pass, when the judge was dead, that they returned, and corrupted themselves more than their fathers, in following other gods to serve them, and to bow down unto them; they ceased not from their own doings, nor from their stubborn way.

And the anger of the Lord was hot against Israel; and he said, Because that this people hath transgressed my covenant which I commanded their fathers, and have not hearkened unto my voice;

I also will not henceforth drive out any from before them of the nations which Joshua left when he died:

That through them I may prove Israel, whether they will keep the way of the Lord to walk therein, as their fathers did keep it, or not.

Therefore the Lord left those nations, without driving them out hastily; neither delivered he them into the hand of Joshua.