he gradual decline of the Latin Empire following Eric's death, in 1216, allowed Theodore I to undertake diplomatic action towards the West. Having married Eric's niece, he sought, after her death, to obtain the regency of the Latin Empire. His efforts were unsuccessful, however, owing to the intervention of the Latin Patriarch and the Venetian baioulos of Constantinople. In an attempt to conciliate the Venetians of the city, he drew up a treaty, in August 1219, granting them commercial privileges on imperial land in Nicaea.

The negotiations for union with the Roman Church were mainly political in nature. These Theodore tried to promote - without success, however, as the idea of union encountered the opposition of almost the entire Greek Orthodox clergy. The ordination by the Patriarch of Nicaea, in 1219, of Sava, brother of Stefan II Nemanja of Serbia, as Archbishop of the autocephalous Church of Serbia, may also be considered a political move. In this way, both the Emperor of Nicaea and the Patriarch were recognised as legal successors to the Byzantine tradition, and the influence of Theodore I on Serbia was enhanced.