The Ottoman Empire was founded by Osman I. As sultan Mehmed II conquered Constantinople (today named Istanbul) in 1453, the state grew into a mighty empire. The Empire reached its apex under Suleiman the Magnificent in the 16th century when it stretched from the Persian Gulf in the east to Hungary in the northwest; and from Egypt in the south to the Caucasus in the north. The empire came to an end in the aftermath of its defeat by the Allies in World War I. The empire was dismantled by the Allies after the war ended in 1918.
With the demise of the Seljuk Sultanate of Rum (c. 1300), Anatolia was divided into a patchwork of independent states, the so-called Anatolian Beyliks. By 1300, a weakened Byzantine Empire had lost most of its Anatolian provinces to these Turkish principalities. One of the beyliks was led by Osman I (d. 1323/4), from which the name Ottoman is derived, son of Ertuğrul, around Eskişehir in western Anatolia. In the foundation myth expressed in the story known as "Osman's Dream", the young Osman was inspired to conquest by a prescient vision of empire (according to his dream, the empire is a big tree whose roots spread through three continents and whose branches cover the sky). According to his dream the tree, which was Osman's Empire, issued four rivers from its roots, the Tigris, the Euphrates, the Nile and the Danube. Additionally, the tree shaded four mountain ranges, the Caucasus, the Taurus, the Atlas and the Balkan ranges. During his reign as Sultan, Osman I extended the frontiers of Turkish settlement toward the edge of the Byzantine Empire.