In the interior of the Serb territory, during the eleventh and twelfth centuries, three political centres came into prominence and shaped themselves into larger territorial units.  These were:  (1) Raska, which had been Caslav’s centre and is considered the birth-place of the Serbian state (this district, with the town of Ras as its centre, included the south-western part of the modern kingdom of Serbia and what was the Turkish sandjak or province of Novi-Pazar); (2) Zeta, on the coast (the modern Montenegro); and (3) Bosnia, so called after the river Bosna, which runs through it.  Bosnia, which roughly corresponded to the modern province of that name, became independent in the second half of the tenth century, and was never after that incorporated in the Serbian state.  At times it fell under Hungarian influence; in the twelfth century, during the reign of Manuel Comnenus, who was victorious over the Magyars, Bosnia, like all other Serb territories, had to acknowledge the supremacy of Constantinople.

It has already been indicated that the Serbs and Croats occupied territory which, while the Church was still one, was divided between two dioceses, Italy and Dacia, and when the Church itself was divided, in the eleventh century, was torn apart between the two beliefs.  The dividing line between the jurisdictions of Rome and Constantinople ran from north to south through Bosnia, but naturally there has always been a certain vagueness about the extent of their respective jurisdictions.  In later years the terms Croat and Roman Catholic on the one hand, and Serb and Orthodox on the other, became interchangeable.  Hercegovina and eastern Bosnia have always been predominantly Orthodox, Dalmatia and western Bosnia predominantly Roman Catholic.  The loyalty of the Croatians to Austria-Hungary has been largely owing to the influence of Roman Catholicism.

During the first centuries of Serbian history Christianity made slow progress in the western half of the Balkan peninsula.  The Dalmatian coast was always under the influence of Rome, but the interior was long pagan.  It is doubtful whether the brothers Cyril and Methodius (cf. chap. 5) actually passed through Serb territory, but in the tenth century their teachings and writings were certainly current there.  At the time of the division of the Churches all the Serb lands except the Dalmatian coast, Croatia, and western Bosnia, were faithful to Constantinople, and the Greek hierarchy obtained complete control of the ecclesiastical administration.  The elaborate organisation and opulent character of the Eastern Church was, however, especially in the hands of the Greeks, not congenial to the Serbs, and during the eleventh and twelfth centuries the Bogomil heresy (cf. chap, 6), a much more primitive and democratic form of Christianity, already familiar in the East as the Manichaean heresy, took hold of the Serbs’ imagination and made as rapid and disquieting progress in their country as it had already done in the neighbouring Bulgaria; inasmuch as the Greek hierarchy considered this teaching to be socialistic, subversive, and highly dangerous to the ecclesiastical supremacy of Constantinople, all of which indeed it was, adherence to it became amongst the Serbs a direct expression of patriotism.