The Bulgarian Orthodox Church spent twelve years split in two, and the case that ended it became a reference point in European law on how far a state may involve itself in a religious dispute.
The origin was the communist period. Patriarch Maxim had been installed in 1971 with the approval of the state, and after 1989 a group of bishops declared his election uncanonical on that ground and formed an alternative synod. The post communist governments then did the thing that turned an internal argument into a legal one: the state registration authority recognised first one synod and then the other as the legitimate leadership, depending on which party held office, and in 2004 the police were used to evict clergy of the alternative synod from around two hundred and fifty churches and hand the buildings to the recognised body.
The alternative synod took the eviction to the European Court of Human Rights, which found against Bulgaria on the ground that the state had not remained neutral. A state may not resolve a leadership dispute inside a religious community by force, whatever the merits of either side, because the freedom of religion protected by the Convention includes the community's freedom to organise itself.
The schism was formally healed after Maxim's death and the election of a new patriarch, and most of the alternative clergy were received back. What survives is the principle: the judgment is cited across the region whenever a government moves to decide which body is the real church, and the same argument has since been rehearsed in Moldova, North Macedonia, Ukraine and the Baltic states.