With the conquest of Constantinople by the Ottoman Turks in 1453, the threat Mehmet II posed to the pocket empire had increased. David's brother John had spent the following years up to his death building alliances to protect the empire, with the Georgian princes to the east and with Uzun Hassan of the Ak Koyunlu, and David seems to have counted on their support. The Muslim rulers of Sinope and Karaman appear to have been enlisted as allies by John or Uzun Hassan.