Judges 21:15

‘ And the people repented themselves for Benjamin, because Yahweh had made a breach in the tribes of Israel.'

All that was done was in the end thought of as done by Yahweh, for He was the God of the covenant and of the tribal confederacy. Thus He was seen as over all that they did, even when He might not have approved of it. It was His law and His holiness that had caused the actions that had brought the breach. But it was the people who had to repent and change their minds so as to allow Benjamin back into the confederacy. It was not God Who had banned them.