Leo XIII, who transformed the Church in the 20th century

In the United States, a very liberal and individualistic movement was gaining ground, while in Europe the challenge of secularization was becoming increasingly pressing. To address these issues, the conclave chose Cardinal Vincenzo Pecci, a respected figure from the Roman papal nobility, known for his talents as a diplomat and administrator.

The man who took the name Leo XIII had been Archbishop of Perugia for 30 years, but was transferred to Rome a year before the death of Pius IX to become Camerlengo, due to poor health. Everyone expected a short pontificate, even the man himself, who ultimately reigned for a quarter of a century, one of the longest in history.

Although he aligned himself with Pius IX's position on the “Roman question,” continuing to denounce the usurpation by the Italian crown, Leo XIII realistically acknowledged the end of the temporal power of the popes and officially dissolved the Papal States in 1900.

Pragmatic, he made gestures of openness towards the Republicans in France and negotiated with Bismarck to end the Kulturkampf. He also showed interest in the development of the Church in the “New World,” in Latin America and the United States, where he condemned “Americanism.”

Very aware of the developments of his time (he was an avid reader of the press and was the first pope to grant an interview), Leo XIII also devoted his time to intense reflection on the Church and society. He wrote 86 encyclicals, a record number.

In 1902, a year before his death, Leo XIII, somewhat in the manner of St. Augustine's Retractationes, drew up a list of his nine most important encyclicals, offering a comprehensive overview of his very dense pontificate as an intellectual pope. The philosopher Étienne Gilson even considered him the “greatest philosopher of the 19th century.”

The first is Æterni Patris (1879), on “Christian philosophy,” which proposes as a solution to modernism a renewed study of St. Thomas Aquinas (neo-Thomism), followed by Libertas Praestantissimum (1888), on human freedom, which condemns the excesses of liberalism. 

Then there is Arcanus Divinae Sapientiae (1880), which explains the Church's condemnation of divorce, Humanum Genus (1884), which attacks the “relativism” of the Freemasons, Diuturnum (1881), on political authority, Immortale Dei (1885), on the Christian constitution of states, which criticizes secularism, and Quod Apostolici Muneris (1878), which condemns socialism.

Next came Leo XIII's most famous encyclical, Rerum Novarum (1891), which, in order to face the challenges of modernity, laid the foundations of Catholic social teaching and what would later become known as the “social doctrine of the Church.” Finally, in Sapientiae Christianae (1890), Leo XIII urged Catholics to refuse to obey civil laws when they contradicted religious teachings.

While Leo XIII's thinking had anti-modern overtones, it also pedagogically promoted a “Catholicism of movement” capable of responding to the challenges of the new era. A man of great curiosity, he was the first pope to have his voice recorded and the first to be filmed.

His important spiritual and intellectual legacy has nourished all the pontificates of his successors, right up to Leo XIV today.

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Earlier in the series: 
Leo the Great 
Leo II
Leo III
Leo IV
Leo V
Leo VI
Leo VII
Leo VIII
Leo IX
Leo X
Leo XI
Leo XII