What can we do to make peace in the world? As Pope John said, it pertains to each individual to establish new relationships in human society under the mastery and guidance of justice and love (cf. John XXIII, Pacem in Terris, [11 April 1963]: AAS 55, [1963], 301-302).

All men and women of good will are bound by the task of pursuing peace. I make a forceful and urgent call to the entire Catholic Church, and also to every Christian of other confessions, as well as to followers of every religion and to those brothers and sisters who do not believe: peace is a good which overcomes every barrier, because it belongs to all of humanity!
…
To this end, brothers and sisters, I have decided to proclaim for the whole Church on 7 September next, the vigil of the birth of Mary, Queen of Peace, a day of fasting and prayer for peace in Syria, the Middle East, and throughout the world, and I also invite each person, including our fellow Christians, followers of other religions and all men of good will, to participate, in whatever way they can, in this initiative. -Pope Francis, Angelus Message for Sunday, September 1, 2013

Let’s pray for an end to violence against all human beings. Everywhere. At every stage of development. Let’s remember that peace begins in our own hearts; our willingness love, to forgive, to see the dignity of every human life — even the unlovable.