The two bojar brothers Petur and Asen used the strongly fortificated area around Tarnovo as basis for an uprising against the Byzantine rule in 1185. Soon most of Eastern Bulgaria had joined the uprising, and Petur was proclaimed Tsar in Tarnovo. This "Second Kingdom" was further stabilised and extended by Tsar Kaloyan, Petur and Asen's 3rd brother. Kaloyan drove the Hungarians out of North-West Bulgaria and signed a peace treaty with Byzantium in 1202. The crusaders took Constantinople in 1204, but were kept out of Bulgaria after a great battle near Adrianople the following year. In 1207 Kaloyan had recaptured most of Macedonia, but was killed during the siege of Salonika.

Bogomils (Friends of God), Greek-Orthodox sect which developed in Bulgaria in the 10th century with strong national and social background. The sect persisted to the 14th century and spread to Byzantium, Serbia, Bosnia, Sicily, North Italy and France. The Bogomil doctrine was dualistic: The material world and the humans within were created by Satan, as opposed to the original spiritual world. The doctrine demanded strong asceticism and rejected marriage, image worshipping and the Christian sacraments. The sect was exposed to hard persecution, and was in 1211 condemned as heretical by a council meeting in Tarnovo. The negative philosophy of the Bogomils contributed to the population’s reduced fighting spirit in the continuous struggles with Bulgaria’s neighbour states.