Empire of Nicaea
Note: Between 1204 and 1261 there was an interregnum when Constantinople was occupied by the crusaders of the Fourth Crusade and the Empire was divided into the Empire of Nicaea, the Empire of Trebizond and the Despotate of Epirus, which were all contenders for rule of the Empire. The Laskarid dynasty of the Empire of Nicaea is considered the legitimate continuation of the Roman Empire because they had the support of the (Orthodox) Patriarch of Constantinople and managed to re-take Constantinople.