Boris I of Bulgaria
In a letter addressed to Domagoj between December 872 and May 873, Pope John VIII complained to Domagoj about the obstinacy of Patriarch Ignatius from Constantinople, who had denied Roman jurisdiction over Bulgaria and appointed a "schismatic" as the Archbishop of Bulgaria. The reason for the Pope's sharing such concerns with Domagoj is that Bulgaria apparently bordered Croatia in some part of present-day Bosnia. At the same time the Pope had regular conversation with Boris I of Bulgaria, warning him of a treachery of the Byzantine priests and bishops working in Bulgaria. The papal project could have been to incorporate Croatian Christianity into the Bulgarian Church under the jurisdiction of Rome, thus encouraging the pro-Roman politics of Boris I of Bulgaria who then ruled much of the Balkans. Another letter was sent in 874 or at the beginning of 875, this time to the Croatian clergy, in which the Pope condemned the capital punishment inflicted on the conspirators who were under the protection of Pope's legate, priest John. The Pope also stated that the priest had nothing to do with the conspirators so he could continue his duties normally.