He was talking about the act of vengeance, and it is a word often used to explain and justify violence.
In the Wars of the Roses for instance, the violent actions of men like Jasper Tudor, Edward IV and John Clifford, were an act of personal vengeance. The death of Edmund of Rutland, who died the same day as his father, the Duke of York, this day in 1460, was an act of revenge that took place following the Battle of Wakefield.
My blog on this subject of vengeance begins:
"Behavioral scientists who have studied revenge scanned the brains of people who had been wronged, the researchers gave these people a chance to punish the wrongdoers. As the victims considered revenge, it was noted that this action caused a notable amount of activity in what scientists call the Caudate Nucleus, an area in the brain that processes rewards, which the researchers equated to same feeling we feel when we smoke or eat chocolate." and continues at: