Hungary

In the early 1200s, Tsar Kalojan of Bulgaria capitalized on Hungary's internal strife, notably the civil war between King Imre and Duke Andrew, to reclaim key fortresses such as Beograd, Branicevo, and Vidin by 1204. Kalojan fortified these southern Danube strongholds, establishing Bulgarian ecclesiastical authority by installing a bishop in Branicevo. His territorial ambitions extended into Serbian lands, including the annexation of Nis in 1203, exploiting the instability in Serbia under Vukan and Stefan. The papacy, attempting to mediate, urged Kalojan to make peace with Vukan, but these efforts were largely ineffective. Kalojan's political strategy included playing Byzantium and the papacy against each other to legitimize his rule, ultimately receiving a crown from a papal legate in November 1204, symbolically recognizing papal supremacy while continuing to assert traditional Bulgarian titles.

Religious tensions also marked this period. Although a synod was held in 1211 to address the Bogomil heresy, evidence suggests the sect was not widespread or threatening at the time. Tsar Boril, Kalojan's successor, maintained a pragmatic approach, allying with both Orthodox and Catholic powers despite his Orthodox zeal. Meanwhile, Serbia experienced internal shifts with Stefan regaining power, though the exact circumstances remain unclear. Hungarian-Serbian relations were strained, with Hungary protesting Stefan's coronation but refraining from major military action, possibly due to King Andrew II's absence on crusade and diplomatic interventions.

The Latin Empire's establishment in Constantinople in 1204 and its ongoing conflicts with Bulgarian and Byzantine successor states influenced regional dynamics. The papacy sought to consolidate Catholic influence, calling on Hungary to crusade against Bulgaria in 1238 under the pretext of combating heresy, specifically targeting the Bogomils. However, these calls were driven more by political motives than genuine religious threats. Concurrently, Hungary was engaged in crusades against Bosnia, which, after the Tatar invasions, reasserted its independence as Hungarian troops withdrew permanently.

The arrival of the Tatars dramatically altered the geopolitical landscape. After conquering Kiev in December 1240 and southern Russia, the Tatars invaded Hungary in April 1241, decisively defeating Hungarian forces at the Battle of the Saj River and forcing King Bela to flee to safety. Their campaign extended through Dalmatia, Serbia, and Bulgaria, causing widespread devastation. Bulgaria, situated directly on the Tatar border, suffered significant damage and was compelled to pay tribute by 1253. The Tatar presence influenced Bulgarian political and social developments for decades, including the settlement of Tatar populations within Bulgaria. The shared threat from the Tatars encouraged Hungary and Bulgaria to improve diplomatic relations and consider joint defense strategies.

Bosnia's fortunes improved as a result of the Tatar invasions, which forced Hungarian military withdrawal and allowed Bosnia to regain lost territories and assert independence. The papacy continued to monitor Bosnia closely, dispatching envoys to investigate the region's religious and political situation amid ongoing Hungarian crusading ambitions.

By the mid-13th century, the complex interplay of crusading ambitions, religious affiliations, and external threats such as the Tatars shaped the Balkans' political landscape. The papacy's hopes for widespread Catholic submission, including the Greeks and Orthodox South Slavs, proved overly optimistic. Bulgaria maintained its Orthodox traditions and resisted papal interference despite nominal submissions. The region remained a patchwork of competing powers, alliances, and shifting borders, with the looming Tatar threat underscoring the need for cooperation among former rivals like Hungary and Bulgaria.