Question: When did the city where the author of Pacem in Terris died become its own country?

Knowledge 1: Pacem in terris
Pacem in terris () was a papal encyclical issued by Pope John XXIII on 11 April 1963 on the rights and obligations of individuals and of the state, as well as the proper relations between states. It emphasized human dignity and equality among all people, and made mention of issues such as the rights of women, nuclear non-proliferation, and the United Nations, all of which it endorsed. It was the last encyclical drafted by John XXIII, who had been diagnosed with cancer in September 1962 and died two months after the encyclical's completion. Biographer Peter Hebblethwaite called it Pope John's "last will and testament". Published on Holy Thursday, the Pope called it his "Easter gift". [SEP] Knowledge 2: Canonization of Pope John XXIII and Pope John Paul II
Pope John XXIII (25 November 1881 – 3 June 1963) and Pope John Paul II (18 May 1920 – 2 April 2005) reigned as popes of the Roman Catholic Church and the sovereigns of Vatican City (respectively from 1958 to 1963 and 1978 to 2005). Their canonizations were held on 27 April 2014. The decision to canonize was made official by Pope Francis on 5 July 2013 following the recognition of a miracle attributed to the intercession of John Paul II, while John XXIII was canonized for his merits of opening the Second Vatican Council. The date of the canonization was assigned on 30 September 2013. [SEP] Knowledge 3: Vatican City
The name Vatican city was first used in the Lateran Treaty, signed on 11 February 1929, which established the modern city - state. The name is taken from Vatican Hill, the geographic location of the state. ``Vatican ''is derived from the name of an Etruscan settlement, Vatica or Vaticum meaning garden, located in the general area the Romans called vaticanus ager,`` Vatican territory''.
Knowledge 1: Pope John XXIII
Pope John XXIII did not live to see the Vatican Council to completion. He died of stomach cancer on 3 June 1963, four and a half years after his election and two months after the completion of his final and famed encyclical, Pacem in terris. He was buried in the Vatican grottoes beneath Saint Peter's Basilica on 6 June 1963 and his cause for canonization was opened on 18 November 1965 by his successor, Pope Paul VI, who declared him a Servant of God. In addition to being named Venerable on 20 December 1999, he was beatified on 3 September 2000 by Pope John Paul II alongside Pope Pius IX and three others. Following his beatification, his body was moved on 3 June 2001 from its original place to the altar of Saint Jerome where it could be seen by the faithful. On 5 July 2013, Pope Francis – bypassing the traditionally required second miracle – declared John XXIII a saint, after unanimous agreement by a consistory, or meeting, of the College of Cardinals, based on the fact that he was considered to have lived a virtuous, model lifestyle, and because of the good for the Church which had come from his having opened the Second Vatican Council. He was canonised alongside Pope Saint John Paul II on 27 April 2014. John XXIII today is affectionately known as the "Good Pope" and in Italian, "il Papa buono". [SEP] Knowledge 2: Canonization of Pope John XXIII and Pope John Paul II
Pope John XXIII (25 November 1881 – 3 June 1963) and Pope John Paul II (18 May 1920 – 2 April 2005) reigned as popes of the Roman Catholic Church and the sovereigns of Vatican City (respectively from 1958 to 1963 and 1978 to 2005). Their canonizations were held on 27 April 2014. The decision to canonize was made official by Pope Francis on 5 July 2013 following the recognition of a miracle attributed to the intercession of John Paul II, while John XXIII was canonized for his merits of opening the Second Vatican Council. The date of the canonization was assigned on 30 September 2013. [SEP] Knowledge 3: Vatican City
The name Vatican city was first used in the Lateran Treaty, signed on 11 February 1929, which established the modern city - state. The name is taken from Vatican Hill, the geographic location of the state. ``Vatican ''is derived from the name of an Etruscan settlement, Vatica or Vaticum meaning garden, located in the general area the Romans called vaticanus ager,`` Vatican territory''.
Knowledge 1: Pope John XXIII
Pope John XXIII did not live to see the Vatican Council to completion. He died of stomach cancer on 3 June 1963, four and a half years after his election and two months after the completion of his final and famed encyclical, Pacem in terris. He was buried in the Vatican grottoes beneath Saint Peter's Basilica on 6 June 1963 and his cause for canonization was opened on 18 November 1965 by his successor, Pope Paul VI, who declared him a Servant of God. In addition to being named Venerable on 20 December 1999, he was beatified on 3 September 2000 by Pope John Paul II alongside Pope Pius IX and three others. Following his beatification, his body was moved on 3 June 2001 from its original place to the altar of Saint Jerome where it could be seen by the faithful. On 5 July 2013, Pope Francis – bypassing the traditionally required second miracle – declared John XXIII a saint, after unanimous agreement by a consistory, or meeting, of the College of Cardinals, based on the fact that he was considered to have lived a virtuous, model lifestyle, and because of the good for the Church which had come from his having opened the Second Vatican Council. He was canonised alongside Pope Saint John Paul II on 27 April 2014. John XXIII today is affectionately known as the "Good Pope" and in Italian, "il Papa buono". [SEP] Knowledge 2: Vatican City
The name Vatican city was first used in the Lateran Treaty, signed on 11 February 1929, which established the modern city - state. The name is taken from Vatican Hill, the geographic location of the state. ``Vatican ''is derived from the name of an Etruscan settlement, Vatica or Vaticum meaning garden, located in the general area the Romans called vaticanus ager,`` Vatican territory''. [SEP] Knowledge 3: Pacem in terris
Pacem in terris () was a papal encyclical issued by Pope John XXIII on 11 April 1963 on the rights and obligations of individuals and of the state, as well as the proper relations between states. It emphasized human dignity and equality among all people, and made mention of issues such as the rights of women, nuclear non-proliferation, and the United Nations, all of which it endorsed. It was the last encyclical drafted by John XXIII, who had been diagnosed with cancer in September 1962 and died two months after the encyclical's completion. Biographer Peter Hebblethwaite called it Pope John's "last will and testament". Published on Holy Thursday, the Pope called it his "Easter gift".

Answer: 11 February 1929