Catholic social teaching, commonly abbreviated CST, is an area of Catholic doctrine concerning matters of human dignity and the common good in society. The ideas address oppression, the role of the state, subsidiarity, social organization, concern for social justice, and issues of wealth distribution. Its foundations are widely considered to have been laid by Pope Leo XIII's 1891 encyclical letter Rerum novarum, which advocated economic distributism. Its roots can be traced to the writings of Catholic theologians such as St. Thomas Aquinas and St. Augustine of Hippo. It is also derived from concepts present in the Bible and cultures of the ancient Near East. According to Pope John Paul II, the foundation of social justice "rests on the threefold cornerstones of human dignity, solidarity and subsidiarity". According to Pope Benedict XVI, its purpose "is simply to help purify reason and to contribute, here and now, to the acknowledgment and attainment of what is just... [The church] has to play her part through rational argument and she has to reawaken the spiritual energy without which justice ... cannot prevail and prosper." Pope Francis, in the words of Cardinal Walter Kasper, made mercy "the key word of his pontificate, ... (while) Scholastic theology has neglected this topic and turned it into a mere subordinate theme of justice." Catholic social teaching is distinctive in its consistent critiques of modern social and political ideologies both of the left and of the right, such as liberalism, communism, anarchism, feminism, atheism, socialism, fascism, capitalism, and Nazism, which have all been condemned, at least in their pure forms, by several popes since the late nineteenth century. Catholic social doctrine has always tried to find an equilibrium between respect for human liberty, including the right to private property and subsidiarity, and concern for the whole society, including the weakest and poorest. It is explicitly both anti-capitalist and anti-socialist, with John Paul II stressing the incompability of Catholic doctrine with capitalism: History The principles of Catholic social doctrine have their roots in the social teachings of the New Testament, the Church Fathers, and the Old Testament and Hebrew scriptures generally. The Church responded to historical conditions in Medieval and Early Modern Europe with philosophical and theological teachings on social justice considering the nature of man, society, economy, and politics. In the era of mass politics and industrialization, Catholic social teaching needed to account for what was called "the social