Pope Leo XIII issues the encyclical Rerum…
May 1891 CE
An open letter passed to all Catholic patriarchs, primates, archbishops, and bishops that addresses the condition of the working classes, it discusses the relationships and mutual duties between labor and capital, as well as government and its citizens.
Of primary concern is the need for some amelioration of "the misery and wretchedness pressing so unjustly on the majority of the working class."
It supports the rights of labor to form unions and rejects socialism and unrestricted capitalism, while affirming the right to private property.
Rerum novarum is considered a foundational text of modern Catholic social teaching.
Many of the positions in Rerum novarum will be supplemented by later encyclicals, in particular Pius XI's Quadragesimo anno (1931), John XXIII's Mater et magistra (1961) and John Paul II's Centesimus annus (1991).