The social and religious upheaval created by the Iconoclast controversy in the Byzantine Empire had little effect on the Church of Macedonia. The sources make no mention of expulsion of monks, while the existence on Mount Athos of hermits in the 9th century suggests that the area was not directly affected by the antimonastic policy of the iconoclast emperors.
On the contrary, it was the iconoclastic policy of Leo III and the consequent worsening of relations with the Pope that brought about the detachment of the prefecture of Illyricum and of the Greek-speaking provinces of Calabria (in Southern Italy) and Sicily from the Church of Rome and their subjection to the Patriarchate of Constantinople in 732; these events were to incite enduring conflicts between the two Churches.
Once Iconoclasm was a thing of the past, the reinvigorated Eastern Churches under the patriarch of Constantinople Photios set about the conversion of the Slavs and Bulgars. Moving spirits in this task were the brothers Cyril and Methodios from Thessalonike; they conceived the Glagonic alphabet for the Slavonic language, into which the liturgical texts and Holy Scripture were translated.
In the mid-9th century the so-called Photian heresy provoked a schism between the two Churches, particularly at the point when the newly formed Church of Bulgaria was incorporated into the increasingly powerful Patriarchate of Constantinople.