last chapter of judges

You wonder who is making these decisions to swear an oath to not give any women over to the Benjamites (of course it was them who killed all the women of Benjamin). Which brought them to the decision of killing any tribe/town who didn't come to the gathering, sparing of course the women to give to the Benjamites.
Yes there wasnt a king but where at least is some sort of structure of leadership? At least someone should come up with the bright idea of consulting God. They did it when attacking the Benjamites.