Revelation 6:10

and they cried with a loud voice, saying, How long, O Lord, the holy and true, dost thou not judge and avenge our blood on those who dwell on the earth?

Revelation 18:20-24

Rejoice over her, thou heaven, and ye saints and ye apostles and ye prophets! for God hath avenged you on her.

Treasury of Scripture Knowledge

Summary

Because thou hast spoiled many nations, all the remnant of the people shall spoil thee; because of men's blood, and for the violence of the land, of the city, and of all that dwell therein.

Bible References

The violence

Revelation 6:10
and they cried with a loud voice, saying, How long, O Lord, the holy and true, dost thou not judge and avenge our blood on those who dwell on the earth?
Revelation 18:20
Rejoice over her, thou heaven, and ye saints and ye apostles and ye prophets! for God hath avenged you on her.