What were the antipopes of the Catholic Church?

At a very basic level, antipopes were caused by political motivations. Secular rulers in Europe, who were often kings and emperors, wanted to exert influence over the Church so that those in power would make decisions that favor them.

As a result, they used their military and political power to forcefully install their preferred candidates as popes. When done successfully, these secular rulers would then use the antipopes to act as their puppets.

However, this interference frequently led to prolonged conflicts and divisions within the Church. 

There were times, however, that challengers to the papal throne were driven by theological, rather than political, motives.

This was often caused by different factions within the Church itself, which held conflicting views on key doctrines and practices.

Over time, these disagreements could escalate into full-blown schisms, with each side supporting its own candidate for the papacy.

In the High Middle Ages, ambitious individual clergymen also contributed to the appearance of some antipopes. These men sought to use the position to grab at personal power and further their own prestige.

They would often be able to do this with the backing of influential supporters. In many cases, these antipopes gained a substantial following, which further complicated efforts to seek a successful resolution to the schism.

Historians have identified more than 30 individuals as antipopes throughout Church history, though the exact number varies depending on which claims are recognized as legitimate.

The idea that there could be antipopes first emerged during the early centuries of the Church. In AD 217, Hippolytus of Rome became one of the earliest to acquire this title, by challenging Pope Callixtus I.

He strongly disagreed with Callixtus over theological issues, particularly concerning the treatment of sinners. Over time, his most ardent followers created a schism within the Roman Church that led to a number of clashes with competing groups.

Eventually, Hippolytus reconciled with the Church and ended his opposition. 

Soon after, another antipope called Novatian opposed Pope Cornelius in AD 251 over Cornelius's lenient stance on readmitting lapsed Christians who had renounced their faith under periods of government persecution.

As a result, Novatian's followers established an entirely separate church that lasted for several centuries. Novatian appointed his own bishops and priests and wrote a number of documents to share his views on different topics.

However, it wasn’t until the 11th century that significant political interference in papal elections became increasingly common.

In particular, the investiture controversy between emperors and kings who sought to influence the appointment of popes led to the emergence of antipopes like Clement III in 1080.

Supported by the powerful Holy Roman Emperor Henry IV, Clement III opposed Pope Gregory VII's reforms. His papacy claim would last until his death in 1100, sustained primarily by imperial power.

As a result, the Church had to grapple with how to maintain its independence from influential secular rulers. 

In the 14th century, the dramatic Western Schism began in 1378 when two rival popes, Urban VI and Clement VII, were elected by different factions within the Church following the death of Pope Gregory XI.

The election of Urban VI as pope was initially accepted, but his abrasive personality soon alienated many cardinals. As a consequence, a faction of cardinals declared his election invalid and elected Clement VII as a rival pope.  

Ruling from Avignon in France, he garnered widespread support from the French nobility.  However, his claim further entrenched the divide within the Church.

This schism divided Europe, with different nations having to choose to support one of the two popes. France and Scotland backed Clement VII, while England and much of Germany supported Urban VI.

For nearly four decades, the schism caused immense turmoil within the Church. With both popes excommunicating each other's followers, the faithful faced confusion and uncertainty.

Over time, multiple efforts to resolve the schism failed, extending the conflict for nearly forty years. Then, the Council of Pisa in 1409 attempted to resolve the issue by electing a third pope, Alexander V.

His election aimed to unify the Church, but instead, it simply led to three concurrent papal claimants.  

The final resolution of the Western Schism came with the Council of Constance, which convened in 1414. By this time, the need for unity had become of critical importance to the church.

In fact, the Holy Roman Emperor Sigismund played a key role in convening the council and securing the cooperation of the rival popes.

When the council met in 1415, it deposed or accepted the resignation of the existing popes, including John XXIII, who had succeeded Alexander V. 

Benedict XIII, who had succeeded Clement VII as the Avignon claimant, refused to resign even after being declared deposed, and continued to assert his legitimacy until his death in 1423, despite being abandoned by most of his supporters.

After prolonged negotiations, Martin V was elected as the sole pope in 1417, effectively ending the schism. This resolution restored stability and unity within the Church, but the conflict had caused significant damage. 

The increasing frequency of challengers to the papal throne caused a number of long-term problems for the church. The existence of competing popes weakened the Church's authority and credibility.

Gradually, the faithful grew increasingly disillusioned with the Church's leadership, which led to concerns over the Church's influence on European society.

Also, maintaining two rival papal courts required substantial resources, which quickly depleted the Church's finances.

With both sides seeking support, they often resorted to selling indulgences and other practices that further damaged the Church's reputation.

Eventually, such financial practices contributed to growing calls for reform. 

Ultimately, many critics saw the frequent division to be a symptom of much deeper issues within the Church, including corruption and moral decay.

As a result, the Council of Constance, which had resolved the Western Schism, also initiated broader discussions on how to reform the church. 

The scars left by the prolonged conflict persisted, which affected Church politics and relations with secular rulers for the next few centuries.

In particular, the authority of the papacy had been severely undermined, leading to a period of weakened papal control over the broader Church.

Gradually, this weakening of papal authority contributed to the conditions that eventually sparked the Protestant Reformation.