Twentieth-century Eastern Europe was a vivid example of what the encyclical Rerum Novarum prophesied. It warned the world that the abandonment of private property in order to make all people equal was morally wrong and economically foolish. Twenty-six years before Russia’s Socialist revolution, Pope Leo XIII stated that socialists were “emphatically unjust, for they would rob the lawful possessor, distort the functions of the State, and create utter confusion in the community.” As Samuel Gregg pointed out in a recent article, Pope Leo saw socialism—whatever its form—as something that corrupted the state; damaged the family; violated legitimate property rights; contradicted the commandment against theft; and, above all, was contrary to divine and natural law. Commemorating Rerum Novarum’s one hundredth anniversary in Centesimus Annus, Saint John Paul II noted that “the prognosis which it suggests have proved to be surprisingly accurate in the light of what has happened since then,” and then he adds: “Pope Leo foresaw the negative consequences—political, social and economic—of the social order proposed by ‘socialism.’” Rerum Novarum displayed the fundamental error of socialism, which Pope John Paul II later called the anthropological error (CA, 13).
Kęstutis Kėvalas, "The Encyclical Rerum Novarum and Its Significance for the Countries of Eastern Europe Today," Journal of Markets & Morality 19, no. 2 (Fall 2016): 447-455