Pope Paul III formally excommunicated King Henry VIII through a papal bull titled 'Eius qui immobilis,' signaling one of the pivotal moments in the history of the English Reformation. The excommunication stemmed from Henry's 1533 annulment of his marriage to Catherine of Aragon, which the Pope refused to sanction. Following that, Henry declared himself the Supreme Head of the Church of England, effectively severing ties with the Vatican. This conflict not only revolved around personal matters but also underpinned political power struggles, namely the extent of papal influence over the English monarchy.

The papal bull outlined the reasons for Henry's excommunication, specifically highlighting his refusal to comply with the Pope's authority. It declared him as a heretic and instructed other monarchs to shun him. At the heart of this conflict was the growing assertion of national sovereignty against the traditional power of the papacy. The excommunication galvanized support for the English Protestant Reformation, encouraging themes of individual interpretation of scripture and direct access to God.

The consequences of this papal decree were profound, affecting both religious practice in England and international relations. Catholic loyalists within England faced increased persecution, while the excommunication pushed Henry to further solidify his break from Rome, leading to more radical reforms within the Church of England. Thus, the events surrounding the excommunication not only reshaped English religion but also initiated changes that influenced political landscapes across Europe for generations.