Revelation 6:10

and they cried aloud, "O Sovereign Lord, holy and true, how long wilt thou refrain from charging and avenging our blood upon those who dwell on earth?"

Revelation 18:20-24

O heaven, rejoice over her! Saints, apostles, prophets, rejoice! For God has avenged you on her now."

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 aloud, "O Sovereign Lord, holy and true, how long wilt thou refrain from charging and avenging our blood upon those who dwell on earth?"
Revelation 18:20
O heaven, rejoice over her! Saints, apostles, prophets, rejoice! For God has avenged you on her now."