Pope Innocent II's excommunication of Roger II of Sicily was a significant turning point in the power struggle within the Catholic Church during the 12th century. Roger II, who had solidified his rule over Sicily and parts of southern Italy, had initially recognized Innocent's papal authority. However, he later aligned himself with Anacletus II, an antipope, which prompted Innocent to take formal action against him. This conflict highlighted the intense political maneuvering of the era, as popes sought to reinforce their authority against powerful regional leaders who challenged their legitimacy.

The excommunication had far-reaching implications, not only for Roger's rule but also for the relationship between the monarchy and the Church. It illustrated the complex interactions between secular and ecclesiastical powers in medieval Europe. Roger's support for Anacletus was seen not just as a theological dispute but as a direct challenge to papal supremacy. Such actions were part of a broader trend where monarchs sought to assert their independence in the face of growing papal influence.

Following the excommunication, Roger II faced increasing pressure from Innocent II, which affected his political standing and reign over Sicily. The conflict intensified the existing tensions between the papacy and the Kingdom of Sicily, influencing future interactions and alignments between rulers and the Church. This episode is essential in understanding the dynamics of power during this period and the role of religious authority in shaping medieval governance.