named as "Tekfurs" were not obedient to the Empire and the habitants were unhappy with high taxes. Osman Bey used this poor Byzantine condition and invaded the Greek Tekhfurs' cities of Karacahisar, Bilecik,Yarhisar and Inegol . On the other hand, the success of Osman encouraged Anatolian Seldjuk Sultan, Alaaddin III. He gave the cities Inonu and Eskisehir under the rule of Osman in 1289. When Alaaddin III was taken to Iran and killed by the Ilhanli Sultan Mahmut Gazan Han, the lack of authority in Anatolian Seldjuk caused the Ottomans independence in 1300 and Osman Bey coined his money.

In 1301, Yenisehir and Kopruhisar were conquered and Byzantine Yenisehir became the Ottoman's capital. The progress of Osman Bey in order to create a powerful state, made Tekhfurs and ByzantineEmpire join forces against him. Tekhfurs of Bursa, Orhaneli and Kestel attacked the Ottomans at "Koyunhisar" in 1302 which was known as the first war between Byzantines and the Ottomans ended with the victory of the Ottomans. Bursa was surrounded step by step after the battle. The city was given by its tekhfur in 1326 to Orhan Bey , the son of Osman Bey.