Revelation 6:10

Then in a loud voice they cried out, "Holy and true Master, how long will you refrain from charging and avenging our blood upon the inhabitants of the earth?"

Revelation 18:20-24

Celebrate over her, O heaven, you saints, apostles, and prophets too, because God has taken vengeance on her for 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
Then in a loud voice they cried out, "Holy and true Master, how long will you refrain from charging and avenging our blood upon the inhabitants of the earth?"
Revelation 18:20
Celebrate over her, O heaven, you saints, apostles, and prophets too, because God has taken vengeance on her for you."