Siege of Constantinople

Following the death of the Latin emperor Robert of Courtenay in 1228, a new regency council headed by John of Brienne was elected. After the catastrophic defeat at the Battle of Klokotnitsa, the threat posed by the Epirote Empire to the Latin Empire was removed. A new threat nevertheless emerged from Nicaea, which began conquering territories in Greece. Emperor John III Doukas Vatatzes entered into an alliance with Tsar Ivan Asen II. In 1235, this led to a joint siege against the Latin Empire.

The siege was unsuccessful. The Latin army, with only 126 knights, defeated the forces of Bulgaria and the Empire of Nicaea. Tsar Ivan Asen II and Vatatzes agreed to continue the siege the following year, but when spring arrived, the Bulgarian ruler sent no troops to Constantinople. After John of Brienne died in 1237, the Bulgarians decided to terminate their agreement with Vatatzes because Ivan Asen might become regent of the Latin Empire. Following the unsuccessful siege, a peace treaty lasting two years was concluded between the two empires.