Continued from above:
The Emperor convened a council in 879 in order to clear up some issues left by the previous council which condemned Photius ten years prior. Pope John VIII sent his legates to this council, attended by 383 bishops (almost three hundred more than the bishops who attended the council ten years prior), where several issues were taken care of. Firstly, Photius was exonerated and rehabilitated (contrary to rumors which persist to this day, Photius died at peace with both the Roman Church and the Eastern Church, although for political reasons which will be explained later, he had been exiled from Constantinople). Secondly the council of 869-870 was declared to be invalid. Thirdly, the council forbade any additions to the Niceno-Constantinopolitan Creed, a definitive blow for those who professed the Filioque (one that was not to last for very long, however). This council was accepted by the papal legates, and the four Patriarchates in the East. Whether Pope John VIII accepted the council is a matter of contention amongst scholars. However, the West’s acceptance of Photius as Patriarch of Constantinople seems to suggest that the council was accepted de facto in the West, only to be repudiated later in favor of the Council of 869-870 in the eleventh century.
Eventually, Basil I grew paranoid and in 883 imprisoned his son, future Emperor Leo VI, and would have even blinded him, had it not been for Photius’ intervention. Emperor Basil I died in a hunting accident in 886, and in that same year, Leo became Emperor (some implicated Leo in the death of his Father). Despite lacking evidence for it, Leo was convinced that Photius had played a part in his removal from power in 883, and so forced him to resign, and sent him into exile in a monastery in Armenia where he would die in 893. It seems, however, that Leo VI eventually had a change of heart towards Photius, rehabilitating his reputation in Constantinople, and allowing his body to be buried within the city after Photius’ death.
Anyway, the point of giving this long story is to show that the dispute between East and West really rested more on the issue of whether the popes were attempting to overstep their canonical boundaries. The East to this day would hold that Pope Nicholas I had far exceeded his canonical prerogatives, while the West I suppose would not view it that way. A similar issue also underlies the events leading to the mutual anathemas of 1054, which largely were an issue of abused primacy (from the Eastern perspective), not of doctrine. It also points out some of the issues which have not been quite as widely explored as the Filioque, which has become quite the whipping boy in “reuninon” councils, including what the nature of Rome’s “primacy” should be (from the Eastern perspective, strict adherence to the canonical prerogatives given to her, which makes for a very weak primacy), and just which council should be regarded as authoritative, the one of 869-870 or the one of 879-880. I’m not sure that I’ve ever seen any definitive answers to these issues like I have to the issue of the Filioque (although even on that issue, we have not reached agreement).