O God, merciful and strong,
who crush wars and cast down the proud,
be pleased to banish violence swiftly from our midst
and to wipe away all tears,
so that we may all truly deserve to be called your children.
Through our Lord Jesus Christ, your Son,
who lives and reigns with you in the unity of the Holy Spirit,
one God, for ever and ever.

Or:

O God, author and lover of peace,
to know you is to live, to serve you is to reign;
defend against every attack those who cry to you,
so that we, who trust in your protection,
may not fear the weapons of any foe.
Through our Lord Jesus Christ, your Son,
who lives and reigns with you in the unity of the Holy Spirit,
one God, for ever and ever.

(From Roman Missal, “In Time of War or Civil Disturbance”)