Throughout the history of the Church, saints, religious communities and dedicated communities of lay people, such as the Beguines of Northern Europe, generously cared for the poor and the sick of society. This service was understood as an expression and continuation of the charity of Christ who healed the sick as part of His public ministry. Jesus instructed His disciples to care for others as a manifestation of their love for Him as He identifies Himself with all those in need (Cf. Mt. 25:31–46; Mk. 16:17–18).
However, although bishops and popes sometimes responded vigorously to particular acts of obvious injustice, until recent times, there was no systematic effort to analyze the structures of society in order to address the root causes of injustice and extensive suffering. There are many reasons for this. Apart from changes of ruling dynasties, changes in society normally came very slowly through gradual evolution, and so many thought that the basic structures of society were immutable, almost as if they were divinely ordained. A good many of the bishops and popes were from the nobility and were themselves in possession of extensive landholdings. The pope was ruler of the Papal States in what is now Italy. Their sympathies and alliances were often with the wealthy and powerful, rather than with the peasants.
What changed? From the 13th century, Europe became progressively more urbanized; society was no longer simply agricultural. In the cities, commerce, banking and universities established new economic bases for society. The American and French Revolutions, at the end of the 18th century, eventually changed the perception that the structures of society were immutable. The industrial revolution very rapidly brought about sweeping social changes, including the creation of a new class of the working poor whose work was often dangerous and whose lives were spent in misery. Activists began to analyze the causes of this new misery. The Communist Manifesto of 1848 condemned private property and the evils of unfettered industrial capitalism, calling for class struggle to end injustice. In many cities of the 19th century Europe, there were attempts to overthrow the ruling classes and create communes. Obviously, this frightened the ruling classes. The institutional Church failed to respond to the excesses of unbridled capitalism and was losing the loyalty of the working class in Europe.
In 1870, Pope Pius IX lost control of the Papal States and the institutional Church had an opportunity to reconsider its position in society. Unfortunately, Pius IX bemoaned the loss of the Papal States and proved incapable of taking advantage of the Church’s new freedom to terminate its reliance on worldly power and wealth in order to take stock of the new situation and to respond vigorously to the needs of impoverished urban workers.

A Call To Social Solidarity
However, his successor, Pope Leo XIII, was aware of the new social realities brought about by the industrial revolution. With the encouragement of many bishops, Leo responded to the plight of exploited urban workers with the 1891 encyclical, Rerum Novarum on the Condition of Labor in which he elaborated on the respective rights and duties of capitalist employers, their workers and the state. Leo recognized the right to private ownership of property but also insisted that the owners had responsibilities and duties with regard to the common good. Just and equitable interrelationships between owners, workers and the state were necessary to create a just society. It is an unjust situation when a few are very wealthy while those whose labor produces the wealth are destitute. Workers have a right to a just wage to support their families and participate in society. The state has an obligation to protect the rights and dignity of workers from unjust exploitation and to uphold all that is necessary for the common good.
In 1920, after the horrors of WW I, Pope Benedict XV wrote the encyclical letter Pacem, Dei munus pulcherrimum (Peace, the beautiful task of God) on Peace and Reconciliation in which he exposed the futility and disastrous nature of war. The Gospel calls for an end to enmity and hatred, mutual forgiveness and authentic reconciliation for the good of all humankind.
Forty years after Rerum Novarum, in 1931, while the world was mired in the economic doldrums of the Great Depression, Pius XI wrote Quadragesimo Anno on the Reconstruction of the Social Order. Pius took up again the principles expounded by Leo XIII establishing the obligation of the state to care for the infirm and needy and to foster a social order that will serve the common good. Pius affirmed the rights of workers to form unions for collective bargaining and to achieve fair labor contracts. He developed the principle of subsidiarity and, without using the word, called for social solidarity. Unrestrained capitalism and totalitarian communism are both threats to society. He also noted the plight of agricultural workers.

International Solutions
In his first encyclical Mater et Magistra of 1961 on Christianity and Social Progress, Pope John XXIII took note of a growing disparity in wealth and development between industrialized nations and the rest of the world. He noted that the economic order is global and called for justice between nations, global solidarity, and respect for the dignity of every human being. For the first time, Church teaching addressed international poverty and the need for international solutions.
Pacem in Terris (Peace on Earth), also by John XXIII, in 1963, after the first session of Vatican II, was the first encyclical addressed to all people of good will. At the height of the “Cold War,” the Cuban missile crisis had evidenced the very real threat of nuclear war. Global peace requires respecting the dignity of all people, the equality of nations and the respective rights and duties of all. Truth, justice, love, and freedom are the foundations of peace. Pacem in Terris further developed Church teaching on the rights and duties of individuals, the common good and the need for effective institutions to support the world community.
Gaudium et Spes, the Vatican II Pastoral Constitution on the Church in the World of Today (1965) addressed nearly every social, cultural and socio–economic issue faced by humanity, with attention to building up the international community, constructing authentic peace and avoiding war. Gaudium et Spes has particular weight because, approved by the bishops of the whole world, it inspired many to work actively for a more just world in which all could live in peace and with dignity.
In 1967, not long after the conclusion of Vatican II, in Populorum Progressio on the Development of Peoples, Pope Paul VI directly related peace to development. Paul VI deplored growing global economic exploitation and the debilitating indebtedness of many nations. Fair trade and global economic justice are necessary for peace and the well–being of all people.
Paul VI followed up with Octogesima Adveniens in 1971. It was a call to action addressed to individual Christians and local Churches. It also directed attention to the degradation of the environment and the duty of all to protect the environment to protect life.

Injustice And Liberation
The Synod of Bishops of 1971 broke new ground with justice in the World. The bishops stated that action, on behalf of justice, is a constitutive dimension of evangelization. If the Church and all its members are not working to free people from oppression of every kind and to create a more just world, then the Church is failing in its essential mission to share the good news of God’s reign with all. The Synod gave strong support to the UN Universal Declaration of Human Rights, UN’s efforts to halt the arms race, rein in commerce of weapons and, to work for the peaceful resolution of conflicts.
In Evangelii Nuntiandi on Evangelization in the Modern World of 1975, Pope Paul VI reiterated the message of the 1971 Synod that efforts to overcome injustice and to foster liberation are essential elements of proclaiming the Gospel.
John Paul II with Laborem Exercens, on the Dignity of Work (1981), Solicitudo Rei Socialis, the Social Concern of the Church (1987) and Centesimus Annus, on the 100th anniversary of Rerum Novarum (1991) continued the tradition. Benedict XVI called for a more holistic understanding of development in Caritas in Veritate (2009).
Those who desire more detailed information on particular justice issues can purchase the Compendium of the Social Doctrine of the Church, by the Pontifical Council for Justice and Peace, 2009, or they can download it for free from the Vatican website. The Catechism of the Catholic Church also presents the official teaching on social justice issues.