Theodore's father-in-law did not abandon his claim to the throne. After being released from prison, AlexiosIII persuaded the Seljuqs to invade Nicaea, but Theodore defeated them in 1211. The Latin Emperor Henry of Flanders captured important fortresses in western Asia Minor in 1212, but he ran out of soldiers and could not place garrisons in them. Henry implicitly acknowledged the existence of the Empire of Nicaea in his peace treaty with Theodore. Theodore conquered western Paphlagonia on the Black Sea coast from AlexiosI of Trebizond. Around 1220, Theodore tried to persuade the Latins of Constantinople to acknowledge his rule, but they refused. Theodore established a powerful state, located in the vicinity of Constantinople, which enabled his successors to expel the Latins from the city and revive the Byzantine Empire in 1261.