Giacomo della Chiesa is elected pope and takes the name Benedict XV

The Swiss theologian Karl Barth publishes his influential Commentary on Romans, taking St Paul's epistle as his text

Ambrogio Ratti is elected pope and takes the name Pius XI

In I and Thou the Austrian theologian Martin Buber interprets religion in terms of the subjective experience of interpersonal relationships

The Lateran Treaty, between the Holy See and the state of Italy, establishes the Vatican City as a free state within the wider nation

Pope Pius XI issues an encyclical, Mit Brennender Sorge, condemning the Nazi ideology of racism

Lutheran pastor Martin Niemöller is arrested for defying the Nazis and spends the next eight years in concentration camps

Eugenio Pacelli is elected pope and takes the name Pius XII

Roger Schutz establishes an ecumenical religious order at Taiz&eachute; in France

The World Council of Churches is established in Amsterdam – a significant step in the ecumenical movement

US evangelist Billy Graham forms the Billy Graham Evangelistic Association, to take the Christian message to the world

Albanian missionary Mother Teresa opens the Nirmal Hriday, or Kalighat Home for Dying Destitutes, in Calcutta

Korean evangelist Sun Myung Moon launches the Unification Church, a mission to unify world Christianity

Civil war breaks out in Sudan between the Muslim north and the Christian south

US novelist Mary McCarthy describes the religious pressures she grew up with in Memories of a Catholic Girlhood

Angelo Roncalli is elected pope and takes the name John XXIII

Pope John XXIII summons a second Vatican Council

Neo-Pentecostalism, also known as Charismatic Renewal, becomes an important element within many Christian denominations

The Second Ecumenical Council of the Vatican begins, 94 years after the start of the First Vatican Council under Pius IX

Pope John XXIII dies, only a few month's after the start of the great Vatican council that he has summoned

Italian cardinal Giovanni Montini is elected pope and takes the name Paul VI

The Second Vatican Council ends, having made some radical changes in the ritual and attitudes of the Roman Catholic church

Pope Paul VI issues the encyclical Humanae Vitae, condemning all methods of artificial birth control

Catholic bishops in Latin America, plagued by oppressive regimes, develop the concept of liberation theology

Italian cardinal Albino Luciani is elected pope and takes the name John Paul I