The coal country of north-eastern Pennsylvania is full of depressed small towns which have been losing population for decades. Today, if the region makes the news, it is for the social problems associated with the American Rust Belt. But at the end of the 19th century, this was a boom area, with immigrants from Europe – Poles, Germans, Italians – flocking there to work the mines.

It was and still is a strongly Catholic area, and reflecting the diversity of its inhabitants, it used to be common for a town to have multiple Catholic churches catering to the different ethnic groups there. But there are also hints of another tradition – onion-domed churches whose names might include “Orthodox” but more often “Greek Catholic”, and with cemeteries whose headstones are inscribed in a mix of Ukrainian, Russian, Slovak and Hungarian.

This mix does not reflect multiple ethnic groups, but the same one. The Rusyns, or Ruthenians, are little-known, and their American descendants mostly assimilated. Coming from the Carpathian mountain region where Ukraine, Poland and Slovakia meet, they are one of those small groups in Eastern Europe whose existence annoys tidy-minded nationalists – in the Soviet Union they were declared not to exist. Their traditional speech is either a separate language or a dialect of Ukrainian, depending on the politics of whomever you ask. And their religion, which looks Eastern Orthodox but is in fact Catholic, in full communion with Rome, is what you might expect from a group in Europe’s cultural borderlands.

The late comic artist Steve Ditko, co-creator of Spider-Man, was a Rusyn from Johnstown, Pennsylvania. And the tightly knit community of Pittsburgh produced the most famous Rusyn-American, Andy Warhol. Despite being a figurehead of the hedonistic 1960s counter-culture, Warhol remained a committed Catholic and a regular Mass-goer, though his faith was so private even his close friends weren’t aware of it. He remained proud of his roots, so that today the two Andy Warhol museums are located not in New York, London or Paris, but in his home town of Pittsburgh and his family’s home town of Medzilaborce in eastern Slovakia.

The Ruthenian Greek Catholic Church is one of 23 Eastern Catholic Churches which are in union with Rome while retaining their ancient liturgical traditions – Byzantine, Coptic, Armenian or Syriac. They have a complex history, founded in the encounter between Western Catholics and Eastern Christians, and marked by exile, repression, decline and rebirth. A few – the Ukrainian Greek Catholics, the Lebanese Maronites, the Syro-Malabar Church of southern India – are millions-strong and well known from their diaspora communities. Others are much smaller and often forgotten.

One unexpected place where Eastern Rite Catholics are found is in Sicily and southern Italy. The region used to have a strong Greek cultural influence, going back to the Roman Empire, but the local Greeks have long been Italianised. Instead, the Byzantine tradition is preserved by the Italo-Albanian Catholic Church, which represents the Arbëreshë, an Albanian-speaking community scattered around dozens of villages, stemming from waves of migration starting in the 15th century.

Francesco Crispi, former prime minister of Italy and one of the key figures in the country’s unification, was an Arbëresh from Sicily and nephew of the Italo-Albanian bishop Giuseppe Crispi. Though out of favour since 1945 due to Mussolini’s praise of his strongman style, Crispi was one of the most significant politicians of his time. Notably, at a time of hostile relations between the Church and the new Italian state, he negotiated with Cardinal Pecci (later Pope Leo XIII) to allow the 1878 conclave to take place in Rome, thus ensuring the papacy’s continuous presence in the city.

The Ethiopian Catholic Church, whose half a million members are still a tiny minority in the country, has a long history but one with many false starts. During the Age of Discovery, Jesuit missionaries from Portugal made contact with Ethiopia’s ancient Christian community and tried to bring it into communion with Rome. Eventually, Emperor Susenyos I was converted and in 1622 declared Ethiopia a Catholic country. This ended 14 years later, when aggressive Latinising from the missionaries led to a public backlash which resulted in missionaries being expelled from the country.

The thread was picked up again in the 19th century by the Italian missionary St Giustino de Jacobis, who was more respectful of local customs and established an Eastern Catholic community which persists today. The Ethiopian Catholics are one of the most distinctive groups in the global Church. They celebrate the Alexandrian Rite Mass in the ancient Ge’ez language, sung in a style of chant called zema, which has been dated to the 6th century. They also have a fasting regime and a kosher-style dietary code which, though not as austere as that of the dominant Ethiopian Orthodox, are much more restrictive than anything in Western Catholicism.

The Eastern Catholic Churches, because of the regions they come from, have often been battered by historical forces. Armenian Catholics were devastated by the genocide of a century ago, and today twice as many Maronites live in the diaspora as in Lebanon. The Eastern Catholics living in Europe’s borderlands have often been harshly treated, but have also given the Church outstanding examples of faith.

Blessed Pavel Gojdič was Bishop of the Greek Catholic Eparchy of Prešov in what is now Slovakia, ministering to the Eastern Catholic faithful of four nationalities – Slovaks, Rusyns, Hungarians and Ukrainians. In 1939, as Nazi Germany was carving up Czechoslovakia, he spoke openly against the persecution of Slovakia’s Jewish minority. This put him on a collision course with not only the Nazis but also the majority of the Slovak Church, then influenced by the anti-Semitism of Mgr Jozef Tiso, head of the Slovak puppet government.

Gojdič did not buckle under pressure, and in 1942 was reported by the Slovak secret police for presiding over fictitious conversions of Prešov’s Jews to save them from deportation. Having survived one form of totalitarianism, he then fell victim to another, as the post-war communist government outlawed the Greek Catholic Church and tried the ailing Gojdič for treason. He died in prison in 1960. Bishop Gojdič was beatified as a martyr by Pope John Paul II in 2001 and honoured as Righteous Among the Nations by Yad Vashem in 2007.

The new frontier among the Eastern Catholic Churches is the Russian Greek Catholic Church, counting around 3,000 members. Even though an exarchate was established in 1917, Soviet repression meant that Eastern Rite Catholics went underground. Their outstanding figure, Mother Catherine Abrikosova, was subjected to a Stalinist show trial and spent more than 10 years in solitary confinement before her death in 1936.

The position of Eastern Rite Catholics in Russia – as opposed to that of Latin Rite Poles or Lithuanians – is still tenuous, with little organisation in place. Their existence remains a flashpoint in Rome’s relations with the Russian Orthodox, who are intensely suspicious of Catholic activity in Russia.

The Eastern Catholic Churches may number only 18 million out of the world’s billion-plus Catholics, but as living links to ancient Christian traditions they enrich the Church enormously. As Pope Leo XIII said in his 1894 encyclical Orientalium Dignitas: “Their antiquity is august, it is what gives nobility to the different rites, it is a brilliant jewel for the whole Church, it confirms the God-given unity of the Catholic Faith.”

Jon Anderson is a freelance writer