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Why had Pope John XXII excommunicated Emperor Louis IV?

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William of Ockham English theologian and philosopher William of Ockham, detail from a stained-glass window, c. 1985; in All Saints' Church, Ockham, Surrey, England.

Pope John XXII excommunicated Emperor Louis IV in March 1324 primarily due to political and jurisdictional conflicts regarding the Holy Roman Empire.12

The tension escalated after Louis IV’s victory at the Battle of Mühldorf in 1322, which alarmed the pope. John XXII, who sought to keep the empire vacant to maintain influence, had appointed Robert of Naples as imperial vicar in Italy vacante imperio (in the absence of an emperor). When Louis sent his own vicar to support the Ghibellines in Milan and Verona, the pope accused him of acting as king of the Romans without papal confirmation and of aiding heretics.12

John XXII ordered Louis to surrender his title within three months, threatening his subjects with excommunication and forfeiture. Louis responded by asserting the independence of the empire and the validity of his election without papal approval, leading to his formal excommunication. This conflict was further exacerbated by the pope's opposition to the Franciscan doctrine of absolute poverty, which Louis supported, and the pope's close alignment with French interests.12