The first decade of Ivan Asen's rule is poorly documented. Andrew II of Hungary reached Bulgaria during his return from the Fifth Crusade in late 1218. Ivan Asen did not allow the king to cross the country until Andrew promised to give his daughter, Maria, in marriage to him. Maria's dowry included the region of Belgrade and Braničevo, the possession of which had been disputed by the Hungarian and Bulgarian rulers for decades.

When Robert of Courtenay, the newly elected Latin Emperor, was marching from France towards Constantinople in 1221, Ivan Asen accompanied him across Bulgaria. He also supplied the emperor's retinue with food and fodder. The relationship between Bulgaria and the Latin Empire remained peaceful during the reign of Robert. Ivan Asen also made peace with the ruler of Epirus, Theodore Komnenos Doukas, who was one of the principal enemies of the Latin Empire. Theodore's brother, Manuel Doukas, married Ivan Asen's illegitimate daughter, Mary, in 1225. Theodore who regarded himself the lawful successor of the Byzantine emperors was crowned emperor around 1226.

Relationship between Bulgaria and Hungary deteriorated in the late 1220s. Shortly after the Mongols inflicted a serious defeat on the united armies of the Rus' princes and Cuman chieftains in the Battle of the Kalka River in 1223, a leader of a western Cuman tribe, Boricius, converted to Catholicism in the presence of Andrew II's heir and co-ruler, Béla IV. Pope Gregory IX stated in a letter that those who had attacked the converted Cumans were also the enemies of the Roman Catholic Church, possibly in reference to a previous attack by Ivan Asen, according to Madgearu.

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.