During the reign of Simeon's successors, Bulgaria was weakened by internal struggles; the heresy of the priest Bogomil spread and influenced the teachings of the Cathars and Albigenses in Western Europe.

After Simeon the Great, marked the "Golden, stronger Byzantium took over several parts of Bulgaria and later on, took full control over the country. In 1018 after prolonged wars, the Byzantine Empire conquered Bulgaria.

In 1186 the uprising led by two boyars, the brothers Assen and Peter overthrew the domination of the Byzantine Empire. The Second Bulgarian Kingdom
 was founded and Turnovo became the new capital. After 1186 Bulgaria was initially ruled by Assen and after that by Peter.  In the years that followed Byzantines suffered many defeats in the southern Bulgarian lands.

The earlier power of Bulgaria was restored during the reign of their youngest brother Kaloyan /1197-1207/ , and during the reign of King Ivan Assen II /1218–1241/, the Second Bulgarian Kingdom reached its greatest upsurge; political hegemony was established in Southeastern Europe, the territory of the country spread to the Black Sea, the Aegean Sea and the Adriatic Sea - the economy and culture developed.

Bulgaria reached a new peak, which lasted until the end of the Second Bulgarian Kingdom /1186-1396/. The schools of literature and the arts in Turnovo developed. The traditions in Bulgarian culture, which is evidenced by the frescoes in the Boyana Church , the churches in Turnovo, in the Zemen Monastery the churches hewn into the rocks near Ivanovo, the miniatures in the Gospel that belonged to King Ivan Alexander   kept at the British Museum  in London and Manassiy's Chronicle. In 1235, the Head of the Bulgarian Church was given the title of Patriarch.

In the shadow of the Ottoman Empire

At the turn of the 13th century the decline of the Bulgarian State started under the threat of a new enemy, the Ottoman Turks . Despite the efforts of the kings, the irreversible process of feudal separation turned the once mighty state into an easy target for the much stronger Turks. The Bulgarian kings and local nobles, as well as the other Balkan rulers failed to demonstrate political farsightedness and to judge soberly the strength and potential of the common enemy. The strife among some of the boyars resulted in the division of Bulgaria into two kingdoms: the kingdoms of Vidin and Turnovo. This weakened the country and it was conquered by the Ottoman Empire in 1396. The Bulgarian people however, offered heroic resistance to the Ottoman Turks  and in practice became one of the most serious barriers to their expansion into the heart of Europe.

In the years that followed the Bulgarians sought to tie up their liberation and resistance actions with the wars waged by the European Christian states and their coalitions against the Ottoman Empire.

For nearly five centuries Bulgaria was under Ottoman domination. The initial years were characterised by sporadic and unorganised attempts to win freedom. Later the appearance of the clandestine fighters, the "Haydouts", made the emergence of a well organised national liberation movement possible. Many uprisings and the “Haydout” movements were initiated as a spontaneous form of armed resistance. Haidout detachments, led by brave and selfless Bulgarian men and women became active in many parts of the country as early as the mid 15th century.