 Complete the following phrase:  He began his reign during a very critical period in the history of the Latin Empire of Constantinople, because the fall of the Kingdom of Thessalonica in 1224 had interposed formidable enemies between the capital of the empire on the one hand and the crusaders states in the Peloponnese on the other. But the defeat of Emperor Theodore Komnenos Doukas of Thessalonica c. 1225-1230 by Tzar Ivan Asen II of Bulgaria 12181241 