Answer
Power struggles over the kingdom and patriarchates plagued Pope Formosus's reign. In particular, he had to contend with the claims of the Holy Roman Emperor Otto I. Formosus's predecessor, Stephen VI, had excommunicated Otto for invading the Papal States. However, Formosus had Stephen's body exhumed and re-tried, finding him guilty of treason and perjury. This act further angered Otto, who forced Formosus to abdicate and had him imprisoned.