Revelation 6:10

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

Revelation 18:20-24

Rejoice over her, O heaven, and ye holy apostles and 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, holy and true, dost thou not judge and avenge our blood on those that dwell upon the earth?
Revelation 18:20
Rejoice over her, O heaven, and ye holy apostles and prophets, for God hath avenged you on her.