Initially, the Ottoman Empire was a coalition of Turkish tribes that grew to be one of the most powerful empires in the world. It controlled the most land during the year 1683. At that time, the sultan, Mehmet the Fourth, controlled all of Asia Minor, Mesopotamia, Syria, Lebanon, Israel, Egypt, parts of modern Saudi Arabia, North Africa, and all of southeastern Europe.
Its decline began in the year 1566 when Süleyman I withdrew from his office as leader and created a new office of Grand Vizier who would stand in his place. The problem with this was that the people did not place their loyalty with the Vizier but with the Sultan. So, the Vizier never had the trust of the people.
The Ottoman Empire was around for more than six hundred years and ended in 1922 when they fought on the losing side during the first World War. When the war ended, Mehmed VI, was deposed, and the empire was split apart.