WIP!
De ecclesia:
The Catholic Church and its woes in the 20th century
Benito Mussolini remained a socialist/communist ITTL and, together with many even more radical comrades, proclaimed the Italian Workers' Republic in late 1917 - the fourth communist state after America (democratically elected and secured after a coup attempt), Britain and France.
While France's first communist revolution quickly collapsed (West France was an an Anglo-American satellite state which is not even recognised as communist by many Lutte Nationale supporters), Italy's was crushed - but not before Robert Brazier's France intervened and helped a fascist "counter-"revolution in late 1935.
During the Decada Rossa ("Red Decade") it was that the most extreme communists around Guglielmo Ventriccio and Emiliano D'Avella came to power, after the death of Benito Mussolini at the hands of an intra-syndical rival on October 19, 1924. When the pope died, Ventriccio ordered the Italian Workers' Army to invade Rome.
Not only were innumerable values of art and culture looted, set on fire or destroyed, the IWA - despite seeing some desertion and even treason - forced the funeral of Pope Pius XI. to take place without a subsequent conclave. Only the fall of the communists in 1935-38 (with French assistance), which ended with the Reds being deposed (some even claim the Ventriccio/D'Avella regime deserves the name "Red Etruscans" or "Red Oscans", but they never claimed any relations to these pre-Roman peoples - it is a reference to the "Red Foula" regime of Guinea decades later), enabled a new conclave to take place in August 1938.
With the fall of Italy to the Allies, the Populist Nationalists were deposed again and Emiliano D'Avella was even restored as the head of the Political Committee of the SULI ("United Workers' Syndicate of Italy") of the Workers' Union of Italy on Sardinia. The island only relaxed on the most extreme form of atheism seen since 9 Thermidor An II (July 27, 1794) - which was valid in all of Italy from 1918 to 1938 (in some parts) and on Sardinia again from 1946 to 1965 - after the death of D'Avella, who was replaced by a more orthodox syndicalist.
The Holy See was vacant for nearly fourteen years (October 19, 1924 to August 7, 1938) - by far the longest it has been in history - and it caused a schism in the church, although it was never openly pronounced. Never was a true antipope proclaimed, let alone a schismatic church.
Before its fall to communism, Mexico recognised the National Populist, French satellite popes (1938-1946). Until 1984, Mexico was under a communist regime (though more often than not shunned or even despised by the UASR as Mexico's communists leaned Zapatist) and recognised the pope in Rome. However, this dramatically changed with the Christian Revolution in 1984: A fundamentalist Catholic Sedevacantist group led this revolution - and managed to spread it to Central America. To this day, the Mexican regime claims the Holy See is vacant (read: occupied by an impostor/usurper) and does not recognsie popes beginning with Paul VII. (Giandomenico D'Azzaro, 1946-1955).
Meanwhile, a "conclave" was called in Buenos Aires in the summer of 1926. But not with the goal of establishing an (anti-)pope, but setting up a "temporary council": This is considered the birth of Episcopalism, i.e. the idea that a council of biships should rule a national Catholic Church in the Pope's stead.
Argentinian, Chilean, Amazonian, Riograndense, Matogrossense, Central American, Cuban etc. Episcopalism formally recognise the Popes from 1929 onwards, but have established a, for all intents and purposes separate from Rome, system of ruling a nation in an authoritarian to totalitarian manner.
In the most extreme versions of Paraguay, Amazonia, Acre and Roramia, laws that have not been applied in Europe since the 1750s, like the penalty of burning at the stake, have been reintroduced - not only for witchcraft and sorcery though...
Mexican and Yucatánian sedevacantist Catholicism, though somewhat less extreme, is still ultraconservative fundamentalist and Ultramontanist in nature as well as fervently anti-communist, especially after the fall of Mexico's communist regime in 1984 in what is known as the Christian Revolution.
Meanwhile in Rome, ever since the election of Paul VII., the papacy has presented a haven of democratic and even reformist values.