You can find a very nice source for understanding Catholic Social Documents from the last 130 years here at the Center for Social Thought

Rerum Novarum (1891 Pope Leo XIII)  Rights and Duties of Capital and Labor,  discusses the relationships and mutual duties between labor and capital, as well as government and its citizens. Of primary concern was the need for some amelioration of “The misery and wretchedness pressing so unjustly on the majority of the working class.” It supported the rights of labor to form unions, rejected socialism and unrestricted capitalism, whilst affirming the right to private property.  Rerum Novarum is considered a foundational text of modern Catholic social teaching.^[7] Many of the positions in Rerum novarum were supplemented by later encyclicals, in particular Pius XI’s Quadragesimo anno (1931),, and John Paul II’s Centesimus annus (1991).

Quadragesimo Anno ( 1931, Pius XI) 40 years after Leo XIII‘s encyclical Rerum novarum. Unlike Leo XIII, who addressed the condition of workers, Pius XI discusses the ethical implications of the social and economic order. He describes the major dangers for human freedom and dignity arising from unrestrained capitalism and totalitarian socialism/communism. He also calls for the reconstruction of the social order based on the principle of solidarity and subsidiarity.

Mater et magistra (1961 John XXIII)

Economic Justice for All (1986)

Centesimus Annus (1991 John Paul II)(100 years after Rerum Novarum 1891)   Written in 1991, during the last days of the Cold War, Centesimus annus specifically examines contemporaneous political and economic issues.  However, the Pope also reserved condemnation for reactionary regimes that persecuted their populations, ostensibly to combat Marxism/communism.  The encyclical expounds on issues of social and economic justice. The encyclical includes a defense of private property rights and the right to form private associations, including labor unions. It compares socialism to consumerism, identifying atheism as the source of their common denial, the dignity of the human person.