Revelation 6:10

They cried out in a loud voice, "Holy and true Master, how long is it to be before you judge the inhabitants of the earth and avenge our blood?"

Revelation 18:20-24

Gloat over her, heaven! and all you people of God, apostles, and prophets, for God has avenged you upon 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
They cried out in a loud voice, "Holy and true Master, how long is it to be before you judge the inhabitants of the earth and avenge our blood?"
Revelation 18:20
Gloat over her, heaven! and all you people of God, apostles, and prophets, for God has avenged you upon her!"