Ottoman Empire

The Ottoman Empire was a Turkish state that ruled over most of the territories of the former Byzantine Empire and beyond, with Constantinople as its capital.

With the in 1453 at the hands of the Ottomans, the  fell. Some time afterwards, the Templars began opposing the Ottoman Empire to conquer it under the Templar banner. Vlad Tepes, Prince of, was one of those that made active attempts at conquering the Ottomans' land, until he was defeated in 1476 by the leader of the Ottoman Assassins, Ishak Pasha, and subsequently killed.

Later in 1509, the Templars returned to the Ottoman Empire under the banner of the Byzantine Empire and the leadership of Manuel Palaiologos, in an attempt to conquer Constantinople from within. While Sultan Bayezid II fought with his son Selim over the succession of the throne, the Templars managed to gain an easy foothold within the Empire, and Bayezid's eldest son and presumed heir, Prince Ahmet, eventually joined the Templars' cause and easily took over Manuel's place as the leader of the Byzantine Templars.

In 1511, due to the combined efforts of Yusuf Tazim, leader of the Ottoman Assassins, Ezio Auditore, Mentor of the Italian Assassins, and Prince Suleiman, the Assassins managed to fight and repel the Templars from the Ottoman Empire, after Manuel's death at the hands of Ezio in Derinkuyu and Ahmet's death at those of his own brother Selim.

Reference

 * Assassin's Creed: Revelations