Pope Leo XIII wrote the encyclical Rerum Novarum as the industrial revolution and political change swept across Europe. The relationship between employers and employees was changing dramatically. Individuals had become wealthy, but most remained poor even though they worked hard. Pope Leo XIII's encyclical spoke of the condition of the working classes during a time when many advocated revolution.
Pope Paul VI wrote the encyclical Populorum Progressio in 1967 to address the world economy and its effect on peoples around the world. At this time many nations saw their economic development stall, while others continued to grow at a record pace. In the document he talks about the rights of workers to a just wage, job security, reasonable working conditions, and to join a worker's association.
Pope John Paul II released the encyclical Evangelium Vitae on March 25, 1995. It deals with the most basic of all principles – the value and sacredness of human life. Our duty to protect life is central to the Christian message. The encyclical is broken into four main chapters which discuss contemporary threats to life, the Gospel's message regarding life, God's law, and hope for a new culture of life.
Quadragesimo Anno was written by Pope Pius XI in 1931 forty years after Pope Leo XIII's Rerun Novarum on the Condition of Workers. He wrote this encyclical to address the ethical challenges facing workers, employers, the Church and the state as a result of end of the industrial revolution and the onset of the Great Depression.
Pope Paul VI wrote the Apostolic letter “Octogesima Adveniens” in 1971 as a letter to Cardinal Maurice Roy, the President of the Council of Laity and of the Pontifical Commission on Justice and Peace on the eightieth anniversary of the encyclical Rerum Novarum. His Holiness sought to highlight many social issues facing people at the time and to inspire renewed action for lay members to participate in social and political reform according to the Gospel.
The encyclical Fides Et Ratio was written by Pope John Paul II to his fellow bishops in 1998 to address the relationship between faith and reason. It was written to support and defend traditional Christian philosophy. His Holiness believed that faith and reason together allow people to know and love God.