Ivan Asen II of Bulgaria
In 1224, the Latin Kingdom of Thessalonica was captured by the Despot of Epirus Theodore Komnenos Doukas, who crowned himself emperor in rivalry to Vatatzes and established the Empire of Thessalonica. It proved short-lived, as it came under Bulgarian control after the Battle of Klokotnitsa in 1230. With Trebizond lacking any real power, Nicaea was the only Byzantine state left, and John III expanded his territory across the Aegean Sea. In 1235, he allied with Ivan Asen II of Bulgaria, allowing him to extend his influence over Thessalonica and Epirus.