Historical background of Osman

Most sources agree that the Ottoman Turks belonged to the Kayı Oghuz Turkic clan, who, according to Ottoman traditions, fled their native homeland in Central Asia, during the early 13th century, due to the Mongol invasions. The clan settled in Anatolia, in a region belonging to the Seljuk Sultanate of Rûm.[17] Other sources claim that the Kayı clan moved to Anatolia two centuries earlier than the previously mentioned date, alongside the Seljuks, when they left Transoxiana to Khurasan around 1040 CE to reside near the city of Merv. Then, the Kayı clan moved towards eastern Anatolia after 1071 CE,[18] where it displaced alongside other Turkic clans. Later, it became involved in the army of Sultan Kayqubad I and fought against the Khwarazmians, Mongols and Byzantines, who were raiding Seljuk lands. According to several sources, the Kayı warriors were known for filling first lines in battles, and their fighting skills and bravery were among the major factors the Seljuks were victorious in many battles. This fact prompted Sultan Kayqubad to appoint Ertuğrul, the clan's Emir, as a Moqaddam (Lieutenant), and to reward the Kayıs some fertile lands near Ankara, where they settled and remained in the service of the Sultan for several years.[19][20]

Later, Ertuğrul was granted dominion over the town of Söğüt in northwestern Anatolia on the Byzantine frontier.[21] He also obtained the title of Uç beyliği or Uç bey (literally: marcher-lord). Granting this title was in line with the traditions of the Seljuk Sultanate, which is rewarding any clan chieftain who rises to power and is joined by a number of smaller clans, the title of marcher-lord. However, Ertuğrul had far-reaching political ambitions. He sought to expand beyond the lands rewarded to him. Thus, he started raiding the Byzantine possessions in the name of the Sultan successfully conquering several towns and villages, and slowly expanding his dominion during the half of the century he spent as a Seljuk governor. In 680 AH / 1281 CE, Ertuğrul died at nearly 90 years of age.[22