"...Pius IX would then pass a month later, leaving the two adversaries dead and the political situation in Italy unclear, bordering on potentially unstable. Upon receiving word of the pontiff's death from Malta, an anonymous cardinal in Rome was said to have quipped, in shockingly profane terms, "Vittorio Emanuele had to go to Hell before His Holiness would deign it time to allow himself to ascend to Heaven." [1]. Immediately, the question of the Maltese Thorn reared its head once again - would the next Pope be elected in Malta, as much of the ultramontanist bloc of cardinals who had joined Pius in exile preferred, or would the Roman Curia that had stayed in the Leonine City and worked for years to mend fences with the Italian Kingdom win out? The question had been addressed somewhat in the months before the Pontiff's passing, when it began to become clear he had little time left in this world, when a French delegation came to Malta to encourage the Church to consider returning to Rome, its proper seat, and accepting the Treaty of Privileges and Guarantees at long last.
The choice of successor to Pius IX made it clear that the Leonine Compromise would win out. Though the conclave was held on Malta - forever known as the Maltese Conclave in Church annals, the one and only - the cardinals selected the moderate camerlengo to Pius IX, Vincenzo Pecci, who had experience in the past as a diplomat and was viewed as the plain choice [2]. In the months ahead, Leo XIII, as he was known, would begin to work with the Italians to fully guarantee the Papal State rights within the Leonine City, and accepted the pressure of five powers to return to Rome - France and Austria, Catholic empires which wanted a solution to the problem and who underwrote the Leonine City's existence; Italy, which despite having a secular leftist government under Angelo Depretis in power wished the issue to go away so the constant feuding between liberals and conservatives in Parliament could end; Britain, where the Conservatives in power viewed the Maltese Thorn as a distraction to a number of more pressing foreign and domestic issues and the resurgent opposition Liberals were fiercely opposed to ultramontanism; and in Germany, where the Kulturkampf of Bismarck had turned the Bavarian and Wurttemburger bishops into ultramontanists and Berlin needed one less faultline between the dominant Prussian state and restive Catholic subjects..."
- Cross and Crown: The Legacy of the Papacy in the Time of the Nation State
[1] Yeah there's probably no way a cardinal would actually say this but whatever, I'm proud of myself for composing it
[2] Pecci's experience as camerlengo, age, diplomatic background and consensus stature makes him win out just like in OTL