Initially, he supported the full communion of the Bulgarian Church with the Papacy and concluded alliances with the neighboring Catholic powers, Hungary and the Latin Empire of Constantinople.

The control of the trade on the Via Egnatia enabled Ivan Asen to implement an ambitious building program in Tarnovo and struck gold coins in his new mint in Ohrid.

He started negotiations about the return of the Bulgarian Church to Orthodoxy after the barons of the Latin Empire had elected John of Brienne regent for Baldwin II in 1229.

Ivan Asen and the Emperor of Nicaea, John III Vatatzes, concluded an alliance against the Latin Empire at their meeting in 1235.

[12] The 13th-century historian, George Akropolites, recorded that Ivan Asen soon fled from Bulgaria and settled in the "lands of the Russians" (in the Principality of Galicia or Kiev).

[13] According to a later source, Ephrem the Monk, Ivan Asen and his brother, Alexander, were taken to the Cumans by their tutor before they moved to the Rus' principalities.

[4][11] Historian Alexandru Madgearu proposes that primarily boyars who opposed the Cumans' growing influence had supported Ivan Asen.

[16] Curta and Fine write that Ivan Asen returned to Bulgaria after Boril's ally, Andrew II of Hungary, had departed for the Fifth Crusade in 1217.

[24] When Robert of Courtenay, the newly elected Latin Emperor, was marching from France towards Constantinople in 1221,[26] Ivan Asen accompanied him across Bulgaria.

[27] Ivan Asen also made peace with the ruler of Epirus, Theodore Komnenos Doukas, who was one of the principal enemies of the Latin Empire.

[28] Theodore's brother, Manuel Doukas, married Ivan Asen's illegitimate[29][citation needed] daughter, Mary, in 1225.

[27][30] Ivan Asen proposed to marry off his daughter, Helen, to the young emperor, because he wanted to lay claim to the regency.

[30] Simultaneously, they offered the regency to the former king of Jerusalem, John of Brienne, who agreed to leave Italy for Constantinople, but they kept their agreement in secret for years.

[34] Only Venetian authors who compiled their chronicles decades after the events–Marino Sanudo, Andrea Dandolo and Lorenzo de Monacis–recorded Ivan Asen's offer to the Latins, but the reliability of their report is widely accepted by modern historians.

[41] They captured Ohrid, Prilep and Serres in Macedonia, Adrianople, Demotika and Plovdiv in Thrace and also occupied Great Vlachia in Thessaly.

[44] He made generous grants to the monasteries on Mount Athos during his visit there in 1230, but he could not persuade the monks to acknowledge the jurisdiction of the primate of the Bulgarian Church.

[52] Pope Gregory IX urged Andrew II of Hungary to launch a crusade against the enemies of the Latin Empire on 9 May 1231, most probably in reference to Ivan Asen's hostile actions, according to Madgearu.

[53] Béla IV of Hungary invaded Bulgaria and captured Belgrade and Braničevo in late 1231 or in 1232, but the Bulgarians reconquered the lost territories already in the early 1230s.

[55] The Orthodox archbishop of Ankyra, Christophoros, who visited Bulgaria in early 1233, urged Ivan Asen to send a bishop to Nicaea to be ordained by the Ecumenical Patriarch.

[57] An agreement about the marriage of Theodore II Laskaris–the heir to the Emperor of Nicaea, John III Vatatzes–and Ivan Asen's daughter, Helen, was concluded in 1234.

[51] After Joachim abandoned his claim to jurisdiction over Mount Athos and the archbishops of Thessaloniki, Germanus recognized him as patriarch, thus acknowledging the autocephaly of the Bulgarian Church.

[64] Taking these events as signs of the wrath of God for breaking his alliance with Vatatzes, Ivan Asen abandoned the siege and sent his daughter Helena back to her husband in Nicaea at the end of 1237.

[67] The marriage resulted in the release of Theodore, who returned to Thessalonica, chased out his brother Manuel, and imposed his own son John as despot.

[66] Pope Gregory IX accused Ivan Asen of protecting heretics and urged Béla IV of Hungary to launch a crusade against Bulgaria in early 1238.

[68] Ivan Asen granted a free passage to the Latin emperor, Baldwin II, and the crusaders who accompanied him during their march from France to Constantinople in 1239, although he had not abandoned his alliance with Vatatzes.

[73] The same source adds, that "A.n.s.khan, the king of Vlachia", who is associated with Ivan Asen by modern scholars, allowed the Cumans to settle in a valley, but he soon attacked and killed or enslaved them.

[77][81] The Synodikon of Tsar Boril and other Bulgarian primary sources referred to her as Anna, suggesting that her name was changed either after she came to Bulgaria, or after she converted to Orthodoxy in 1235.

[86] There is moot evidence[clarification needed] that the Bulgarian church opposed the marriage and that a patriarch (called either Spiridon or Vissarion) was deposed or executed by the irate tsar.

[89] Irene gave birth to Akropolites characterized Ivan Asen as "a man who proved to be excellent among barbarians not only with regard to his own people but also even with respect to foreigners".

[98] The minority of Ivan Asen's successor gave rise to the formation of boyar factions and the neighboring powers quickly conquered the peripheral territories.