The decision by Pope Leo XIV to excommunicate members of the Society of Saint Pius X (SSPX) is the latest twist in a long-running saga between the Vatican and this contentious traditionalist group. It is yet more evidence of the deep polarisation between conservatives and progressives within the Catholic church.The Vatican issued a statement on July 2 to the effect that SSPX had “committed an act of a schismatic nature” by ordaining four bishops the previous day at a ceremony in Écône, the village in Switzerland where SSPX was founded in 1970. The society was established and named after Pope Pius X by the controversial French archbishop Marcel Lefebvre. He was an adherent to the uncompromising positions Pius (who reigned from 1903 to 1914) held against “modernism” – the attempts by some Catholics to apply contemporary intellectual and moral trends to the teachings of the church.In 1907, Pius X had declared modernism to be an attack on all elements of the church by those who “vaunt themselves as reformers”. Those who joined the SSPX reacted specifically to reforms brought about within the church by the Second Vatican Council (often known as Vatican II).Convened between 1962 and ’65, Vatican II was reportedly described by Pope John XXIII as an attempt to “open the windows and let in the fresh air”. It sought to recognise the rapidly shifting world of the 20th century, and reaffirm the role of the church in guiding Catholics by interpreting these events “in the light of the Gospel”. Many reforms occurred within the church as a result, including the introduction of worship in vernacular languages, replacing the older Latin Mass (often referred to as the “Tridentine Mass”, as it was standardised after the Council of Trent in the 16th century). Lefebvre and his supporters saw this as a Modernist revolution. But they were the ones who came under suspicion for this divergence in such important matters of dogma. In 1975, the society was “suppressed”, meaning it was no longer recognised by the Church as legitimate. This proved the start of a much longer struggle, as members of the SSPX continued to act regardless of instruction from the Holy See.In 1976, Pope Paul VI described Lefebvre and his movement as suffering from “a bitter deafness” which had placed them “outside of obedience and communion with the Successor of Peter and therefore of the Church”. He implored them to “reflect calmly, without prejudice” and “to become aware of the deep wounds they otherwise cause the Church”. “We invite them again to think,” he concluded. But his appeal appeared to fall on deaf ears. The struggle between the SSPX and the Vatican boiled over in 1988 when – as at the ceremony a few days ago – four priests were consecrated as bishops at Écône. The event occurred despite a warning from John Paul II, and resulted in the excommunication of Lefebvre and the four bishops. The pope viewed the act as a grave disobedience not only against his authority, but “the unity of the Church”. But as a concession, he acknowledged the “feelings of all those who are attached to the Latin liturgical tradition”, and opened a commission to attempt to return those in the SSPX to the church while “preserving their spiritual and liturgical traditions”. An acknowledgement of a wider conservative desire to retain the Latin Mass and the forms of worship used before Vatican II came in 2007, when Pope Benedict XVI decreed that these older forms could be celebrated under specific conditions.Two years later, Benedict lifted the excommunication of the four bishops from 1988, believing a productive dialogue had emerged. Talks continued between the SSPX and the Vatican in the hope of achieving a reconciliation.In 2012, however, the Vatican declared: “We cannot put the Catholic faith at the mercy of negotiations. Compromise does not exist in this field. I think that there can now be no new discussions.”Discussions did in fact continue during the papacy of Francis, but the SSPX was considered to have “departed from communion with the Church”. Archbishop Gerhard Müller, head of the Congregation for the Doctrine of the Faith which decides matters of doctrine, said that “they must change their attitude and accept the Catholic Church’s conditions”.A Church dividedThe decision by Leo XIV to excommunicate the SSPX follows several months of warnings from the Vatican not to proceed with the consecration of the new bishops.In a letter addressed to Father Davide Pagliarani, superior general of the SSPX on June 30, Leo wrote: “I urge you to consider carefully the spiritual good of the faithful, because the schismatic act you are about to undertake would deprive them of the licit and, in some cases, even valid reception of the Sacraments, which they love and seek for their sanctification.”But the SSPX proceeded and the pope has acted.This episode reflects the considerable tension among conservative Catholics over the reforms of Vatican II. While the size of the SSPX is tiny compared with the global number of Catholics (some 600,000 members in a global community of 1.4 billion), the polarisation of opinions within the church are arguably of a much larger scale.Pope Francis recognised as much in 2022, when – to mark 60 years since the opening of Vatican II – he argued for the need to “overcome all polarisation and preserve our communion” in light of divisions since the 1960s. While Leo XIV is still relatively early into his pontificate, the renewed excommunication is a stark reminder that polarisation remains a pressing issue for the Catholic church, particularly when it comes to modernisation. But like the saga of the SSPX, this issue shows no sign of resolving itself anytime soon.Liam Temple does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.