Revelation 6:10

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

Revelation 18:20-24

Rejoice over her, O Heaven! Rejoice, ye saints, apostles, prophets! For God has now avenged you.

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 with a loud voice they cried, saying, "O Master, holy and true, How long dost thou not judge And avenge our blood On those who dwell on the earth?"
Revelation 18:20
Rejoice over her, O Heaven! Rejoice, ye saints, apostles, prophets! For God has now avenged you.