The Principality of Achaea or of the Morea was one of the three vassal states of the Latin Empire which replaced the Byzantine Empire after the capture of Constantinople during the Fourth Crusade. It became a vassal of the Kingdom of Thessalonica, along with the Duchy of Athens, until Thessalonica was captured by Theodore, the despot of Epirus, in 1224. After this, Achaea became for a while the dominant power in Greece.