Emperor Basil, seeking to confirm his deposition of Photios, patriarch of Constantinople, convenes the Fourth Council of Constantinople in 869-870, which issues no new dogmatic decisions and whose principal action is to restore Ignatius by deposing Photi0s for usurping his ecclesiastical position.

Bulgaria is formally placed under the nominal ecclesiastical jurisdiction of the patriarch of Constantinople but receives an independent archbishopric.

This has significant results both for the Balkan principalities and for the Orthodox Church, as well as greatly strengthening imperial Greek influence in the south Slav world.

The council greatly contributes to the growing rift between the Eastern and Western churches.

(The Roman church will eventually recognize it as the eighth ecumenical council, but the Eastern church for the most part will deny its ecumenicity and continue to recognize only the first seven ecumenical councils.)

The Romans had taken the offensive in the age-long struggle between Christian and Muslim on the eastern borders of Asia Minor from the mid-ninth century onward.

Basil, taking advantage of turmoil within the Muslim caliphate, has continued the attacks made during Michael III's reign against the Arabs and their dualistic Christian allies, the Paulicians.

Basil initiates a war of expansion in 871 by dispatching an army to the upper Euphrates River at Samosata (Samsat).

Raids across the eastern frontier into the Euphrates region continue, though …

…Basil does not manage to take the key city of Melitene.

The power of the Paulicians, considered by Constantinople to be dangerous and heretical, has grown to great extent on the borders of the Armenian province in Asia Minor under the sects' current leaders, Karbeas and Chrysocheir, who are crushed militarily by 872, largely owing to the efforts of Basil's son-in-law Christopher.

Many Paulicians flee Anatolia for the Balkans as the empire expands eastward toward the Euphrates.