Judges 20-21

It took me about 10 minutes to finish this book. This is the conclusion of the story about the sinfulness of the men of Gibeah in the inheritence of Benjamin. I don't understand why the leaders of that tribe stood with their sinful brothers and fought against Israel. I don't under stand why wayward Israel rallied to the side of righteousness because of this act of savagery. Unless it was early in the time of judges and most of Israel was not living in disobedience to God's law. Verse 20:27 gives the time period for this story. It seems to have happened shortly after Joshua's death, rather than just before Samuel's birth. I say that because it refers to Phinehas the grandson of Aaron. I do understand the actions of the leaders and army of Israel. They were seeking to do what was right before God. To purge the evil from Israel.
Stuart