This was viewed with disfavour by the Greeks, and they still called Peter
only _arch[=o]n_ or prince (_knyaz_ in Bulgarian), which was the utmost
title allowed to any foreign sovereign. It was not until 945 that they
recognized Peter as _basileus_, the unique title possessed by their own
emperors and till then never granted to any one else. Peter's reign was
one of misfortune for his country both at home and abroad. In 931 the
Serbs broke loose under their leader [)C]aslav, whom Simeon had captured
but who effected his escape, and asserted their independence. In 963 a
formidable revolt under one Shishman undermined the whole state fabric. He
managed to subtract Macedonia and all western Bulgaria, including Sofia
and Vidin, from Peter's rule, and proclaimed himself independent _tsar
(tsar_ or _caesar_ was a title often accorded by Byzantium to relatives of
the emperor or to distinguished men of Greek or other nationality, and
though it was originally the equivalent of the highest title, it had long
since ceased to be so: the emperor's designations were _basileus_ and
_autocrat[=o]r_). From this time there were two Bulgarias--eastern and
western. The eastern half was now little more than a Byzantine province,
and the western became the centre of national life and the focus of
national aspirations.

Another factor which militated against the internal progress of Bulgaria
was the spread of the Bogomil heresy in the tenth century. This remarkable
doctrine, founded on the dualism of the Paulicians, who had become an
important political force in the eastern empire, was preached in the
Balkan peninsula by one Jeremiah Bogomil, for the rest a man of uncertain
identity, who made Philippopolis the centre of his activity. Its principal
features were of a negative character, and consequently it was very
difficult successfully to apply force against them. The Bogomils
recognized the authority neither of Church nor of State; the validity
neither of oaths nor of human laws. They refused to pay taxes, to fight,