The initial expansionist ambitions of the Latin Empire were crushed only one year after its foundation after the Battle of Adrianople in 1205, where its Emperor Baldwin I was captured and most of his knights perished.

Their Doge took the title quartae partis et dimidiae totius imperii Romaniae dominator or "Lord of a quarter and a half part of the whole Roman Empire".

Emperor Baldwin I was captured, Count Louis I of Blois was killed, and the Venetian Doge Enrico Dandolo led the surviving portions of the crusader army into a hasty retreat back to Constantinople, during the course of which he died of exhaustion.

Whereas in the past the Bulgarian emperor, Kaloyan, had limited his oppression to the aristocracy, his later campaigns included wholesale transfer of populations from the captured cities to distant regions in Bulgaria.

The Bulgarians besieged Adrianople twice, but failed to take the city because of the withdrawal of their Cuman cavalry, and the determined advance of the new Latin emperor, Baldwin I's brother Henry of Flanders.

Seeking to take advantage of that situation, Kaloyan advanced on the city and besieged it with a large force, but was murdered by his own Cuman commander Manastăr at the beginning of October 1207.

Despite the defeat, Boril managed to retain his main forces and continued to campaign against the Latins, reaching in some daring actions the vicinity of Constantinople, a clear evidence of the positions he had regained in the Balkans.

By 1231 the Latin regency had finalized negotiations with John of Brienne, the former king of Jerusalem, who was invited to step in as the guardian and co-emperor of Baldwin II at Constantinople.