The short answer is Pope Pius XI in 1925. The long answer concerns why he did it. It helps to know the situation of his time. Before Italy became a sovereign nation in the late 1800s, popes had ruled over actual geographical territory for centuries. The papal states were erased permanently with the fall of Rome in 1870, leaving then-Pope Pius IX a prisoner of the Vatican. Four popes later, the so-called “Italian Question” was still unresolved. What tangible territory, if any, could the Roman Church claim?
At the time of Pius XI’s election, Mussolini was in power. The new pope surprised the world by emerging on the balcony of St. Peter’s to offer his first blessing urbi et orbi: “to the church and to the world.” No pope had done this since 1870. It signaled his papacy’s willingness to engage as a force in world affairs. Pius XI was convinced the church had to possess some clearly defined temporal power to operate effectively.
Negotiations with Mussolini’s government took place in back channels, resulting in the Lateran pacts of 1929. These defined the Holy See’s independence from Italy, creating the tiny state of Vatican City as a political entity. The pacts included a small financial concession from the Italian government for the loss of the papal states. It defined relations between Vatican City and Italy for the future.
Mussolini had imagined the agreements left him with the upper hand over a subordinated church to which he’d thrown a modest bone. When Pius later attacked fascism in a bold encyclical, Mussolini was caught off guard. That a librarian-cleric-turned-pope could be a public force to be reckoned with hadn’t figured in the dictator’s plans. He might have paid more attention to Pius’ urbi et orbi blessing. And to the institution of the Feast of Christ the King early in his papacy.
Proclaiming Christ as King was, to Pope Pius XI, a clarification of the relationship between the church and temporal affairs. Though men like Mussolini, Stalin, and Hitler ascended to seats of worldly domination in Pius’ generation, the throne of Christ superseded their grasp. As long as Christ reigns, princes of the world are assured no more than a season of power. We as church continue to affirm this truth on the last Sunday of every church year.
Scripture: Pss. 93, 95-99; Isaiah 9:5-6; 43:15; Zephaniah 3:15; Matthew 2:1-6; 4:17; 27:37; Luke 23:42: John 18:33-37; Timothy 4:1; 2 Peter 1:11; Revelation 1:5
Books: The Liturgical Year, Vol. 3: Sundays Two to Thirty-Four in Ordinary Time, Adrien Nocent (Liturgical Press, 2013)
The Popes: Histories and Secrets, by Claudio Rendina (Seven Locks Press, 2002)