Resurrected Bulgaria occupied the territory between the Black Sea, the Danube and Stara Planina, including a part of eastern Macedonia, Belgrade and the valley of the Morava. It also exercised control over Wallachia^[29] Tsar Kaloyan (1197–1207) entered a union with the Papacy, thereby securing the recognition of his title of "Rex" (King) although he desired to be recognized as "Emperor" or "Tsar" of Bulgarians and Vlachs. He waged wars on the Byzantine Empire and (after 1204) on the Knights of the Fourth Crusade, conquering large parts of Thrace, the Rhodopes, Bohemia, and Moldavia as well as the whole of Macedonia.

In the Battle of Adrianople in 1205, Kaloyan defeated the forces of the Latin Empire and thus limited its power from the very first year of its establishment. The power of the Hungarians and to some extent the Serbs prevented significant expansion to the west and north-west. Under Ivan Asen II (1218–1241), Bulgaria once again became a regional power, occupying Belgrade and Albania. In an inscription from Turnovo in 1230 he entitled himself "In Christ the Lord faithful Tsar and autocrat of the Bulgarians, son of the old Asen".

The Bulgarian Orthodox Patriarchate was restored in 1235 with approval of all eastern Patriarchates, thus putting an end to the union with the Papacy. Ivan Asen II had a reputation as a wise and humane ruler, and opened relations with the Catholic west, especially Venice and Genoa, to reduce the influence of the Byzantines over his country. Tarnovo became a major economic and religious centre—a "Third Rome", unlike the already declining Constantinople.^[30] As Simeon the Great during the first empire, Ivan Asen II expanded the territory to the coasts of three seas (Adriatic, Aegean and Black), annexed Medea - the last fortress before the walls of Constantinople, unsuccessfully besieged the city in 1235 and restored the destroyed since 1018 Bulgarian Patriarchate.

The country's military and economic might declined after the end of the Asen dynasty in 1257, facing internal conflicts, constant Byzantine and Hungarian attacks and Mongol domination.^[31] Tsar Teodore Svetoslav (reigned 1300–1322) restored Bulgarian prestige from 1300 onwards, but only temporarily. Political instability continued to grow, and Bulgaria gradually began to lose territory.