Published by Pope Pius XI in 1931, forty years after Rerum Novarum (hence its name, “In the Fortieth Year”), Quadragesimo Anno renewed Leo XIII’s teaching in the midst of the Great Depression and the rise of both communism and fascism.

Its most enduring contribution is the principle of subsidiarity: that matters should be handled by the most local community competent to handle them well, and that larger bodies — including the state — should help smaller communities rather than absorb them. Pius applied this against both unrestrained capitalism, which he warned concentrates wealth and power, and collectivism, which swallows civil society.

The encyclical called for the reform of the social order toward justice and charity, defended a wage sufficient to support a family, and encouraged the intermediate associations that stand between the individual and the state. It gave Catholic social thought much of its vocabulary: subsidiarity, the common good, social justice.

Read the full text at Vatican.va.