In Judges 19:20-30, a Levite is faced with the rape of his concubine and the tribes of Israel destroy the tribe of Benjamin over it. Why?
This happened because:
1) The rape was particularly depraved and shocking. It was a gang rape which went on for hours. The victim was severely injured and died.
2) At the time of the rape both the Levite and his wife were under the protection of a city resident. Taking her away by force and raping her violated a sacred principle of Eastern hospitality. Compare this incident to the similiar one in Genesis 19 where Lot stands in front of his house facing down a rape gang and offers his daughters as victims to save the guests. In a culture which placed the safety of the guest well above the safety of the host and his family, the thought that sacred hospitality had been violated would create outrage.
3) The husband of the dead woman immediately launched a publicity compaign to create widespread outrage.
4) According to the Mosaic law (Leviticus 20:10, Deuteronomy 22:23--27) a man who raped another man's wife or betrothed was to be stoned to death as an adulterer. In line with the principle at Exodus 21:18--19 it was probably also a murder since the victim died soon after the assault.
5) The Benjaminites appearently did not take any judicial action to punish the guilty. Guilt for murder was on the whole community until the murder was brought to justice or the elders swore at a public ceremony that they could not identify him. (Deuteronomy 21:1--9)
6) The Benjaminites refused to hand over the guilty to death. Why is not stated, but one factor may be that an army was camped nearby to back up the demand. Since they were known as excelent warriors, this may have hurt their pride.
7) The Benjaminites not only refused to hand over the guilty but actually went to war to defend them from the force sent to arrest them.
So it appears that out-of-control feelings quickly made a bad situation much worse.
As a side note, this is one of those times where the Bible reports what God's people did without discussing whether he entirely approved or not. Things might have ended very differently if other tribes had approached Benjamin more diplomatically. I have sometimes wondered if that is why before the first two battles God told them to go ahead and fight but did not promise to help them. He may have felt that they shared part of the blame for the impending tradgedy. But still the Benjaminites had much greater guilt because by their actions they had condoned a very serious crime and shifted the responsibility onto their entire community. Likely that is why God finally let the other tribes nearly wipe them out.