Leo XIII
Pope from 1878 until his death (1810–1903), born Vincenzo Gioacchino Pecci in Carpineto Romano into a noble family, educated by the Jesuits and later apostolic nuncio to Belgium and archbishop of Perugia, he was the pontiff who guided the Catholic Church toward modernity after decades of suspicion and confrontation with the liberal and industrial world begun under his predecessor Pius IX. His pontificate, one of the longest in the Church's history, combined intellectual openness with doctrinal firmness: in Aeterni Patris (1879) he decreed the revival of Thomism, the systematic study of Thomas Aquinas, as the Church's official philosophical basis, an impetus that gave rise to Neo-Thomism, a philosophical current that would dominate Catholic thought for over a century and spurred the creation of numerous pontifical academies and universities devoted to its study. His most far-reaching historical contribution is Rerum Novarum (1891), the foundational encyclical of modern Catholic social doctrine, written in response to the 'social question' raised by industrialisation: it defends workers' right to a just wage and to unionisation, harshly denounces inhumane working conditions and unrestrained capitalist exploitation, yet at the same time rejects socialism and class struggle as solutions, instead defending private property as a natural right and proposing a middle way based on collaboration between classes, the principle of subsidiarity, and moderating state intervention —a document that directly inspired the Catholic trade union movement, Christian democracy and the social policies of a good many European countries throughout the twentieth century. Leo XIII also promoted a cautious diplomatic rapprochement with Europe's liberal governments and encouraged the study of the sciences, opening the Vatican archives to researchers.