After the remarkable rule of Simeon, Bulgaria fell into decay. Many historians tend to blame the successor of Simeon the Great, Tsar Peter I, for the decline of the country. They describe him as weak, sickly, meek and unstatesmanlike. Indeed, he did not have his father's dash, his abilities as a military commander, his diplomatic skill or his immense erudition. Yet that quiet and modest monarch remained on the throne longer than any other medieval Bulgarian ruler: from 927 to 970.
The reason for Bulgaria's unhappy lot should not be reduced to the faults of Simeon's son. While many years of wars led to an unprecedented expansion of the state, the peasantry, which constituted the main source of soldiers for the army, was depleted. Human losses, suffering, taxes and the draining of the nation's vital resources was the price Bulgaria paid for the victories of Simeon the Great.
Under Peter I the boyars and the higher clergy amassed wealth, while the general population grew poorer. Hermits who defied the church dwelled in the mountains. A priest of the name of Bogomil spread a teaching which was to accumulate the contempt for the tsar, the boyars and the clergy for centuries. Bogomilism repudiated the state and the church, believing them to be a creation of Evil, of Satan. The numerous followers of Bogomilism were disastrous for state order, while famine, droughts and boyars' unrest were undermining the power of the state.
To the profound distress of the tsar, two plots against him were organized by his own brothers. He found no support in the boyars, either. Simeon's nobles accused him of reconciling with Byzantium's supremacy and of making no plans for expansion. Others, however, insisted that the state would thrive and prosper in peace with Byzantium.
Bulgaria also faced a number of external enemies that Tsar Peter was unable to handle. At the very beginning of his reign he lost the Serb lands. As a result of fierce Hungarian onslaughts from the north, Bulgaria lost important territories beyond the Danube, including the rich Transylvania. The Danube became the northern border of the state, and the Pechenegs repeatedly raided and plundered Dobroudja.
Relations with Byzantium at the time were basically peaceful, as immediately after ascending the throne in 927, Tsar Peter married the grand-daughter of Emperor Romanus Lecapenus. A thirty-year peace treaty was signed, acknowledging the title of Tsar for the Bulgarian ruler. However, this was far from the grandeur Simeon the Great had dreamed of. The treaty never kept Constantinople from thwarting the efforts of Bulgarian diplomacy and encouraging Bulgaria's enemies.
By the end of Peter's rule, Bulgarian-Byzantine relations were on the verge of severing. The tsar's two sons, Boris and Roman, were taken hostages in Constantinople. The machinations of Emperor Nicephorus Phocas incited Prince Svyatoslav of Kiev to attack Bulgaria's northeastern border. Tsar Peter's army suffered a defeat in Dobroudja, which fell under Russian rule. The Russian army took some eighty fortresses and Prince Svyatoslav set up his headquarters in Preslavets. Upon hearing that the Russians were pillaging Bulgarian lands, the tsar suffered a stroke and took monastic vows. Soon afterwards he died and was canonized by the Bulgarian Orthodox Church.