John III Doukas Vatatzes
After Robert of Courtenay died in 1228, a new regency under John of Brienne was set up. After the disastrous Epirote defeat by the Bulgarians at the Battle of Klokotnitsa, the Epirote threat to the Latin Empire was removed, only to be replaced by Nicaea, which started acquiring territories in Greece. Emperor John III Doukas Vatatzes of Nicaea concluded an alliance with Bulgaria, which in 1235 resulted in a joint campaign against the Latin Empire.