Osman I
Fall of the Seljuk Sultanate of Rûm, and the Osmanic Beylik's independence

Osman aspired, after his multiple victories, to expand on two axes, aiming to isolate the Byzantine cities he was looking to conquer. First, he blocked the road leading to İznik from the eastern side. Then, he advanced from the west towards Lopadion and Evrenos. After that Osman turned around Mount Uludağ from both north and south, avoiding the fortified city of Bursa, connecting with his Muslim neighbours in the southeast. During that time, the Byzantine Empire was preoccupied with ongoing clashes with its powerful enemies in Anatolia, such as the Germiyanids and the coastal beyliks, not to mention suppressing unrest and discord in Constantinople and the Balkans. The Empire was unable to face Osman's threats, thus, he felt free to expand at the Byzantines expense exploiting the current situation. At the same time, the Seljuk Sultanate of Rûm was seeing its final days. The Sultanate grip was slowly weakened over its Turkoman Beyliks. Sultan Alâeddin Kayqubad III became deeply unpopular after he purged the Seljuk administration of his predecessor's men with extreme violence. This prompted the Mongol Ilkhan Mahmud Ghazan to call upon Kayqubad to appear before him, and once the latter did in 1302, he was executed and replaced with his predecessor Ghiyāth ad-Dīn Mas'ūd bin Kaykāwūs to keep the peace in Anatolia. According to another account, Mongol and Tatar hordes raided Asia Minor in 1300, and killed Sultan Kayqubad in his capital Konya. It was also said that Kaykāwūs himself killed his rival, coveting his own return on the throne. Another story suggests that Kayqubad escaped and sought refuge in the Byzantine court where he remained until his death. In all cases, Kaykāwūs's rule was short-lived, lasting between 4 and 6 years at most, and when he died in 1308 CE, the Seljuk Sultanate of Rûm was no more to be mentioned in the historical records, giving the way for the Turkoman beyliks to emerge as independent states.

The demise of the Seljuk Sultanate of Rûm gave Osman autonomy over his dominion, he soon dubbed himself Padişah Āl-ıʿOsmān (sovereign of the house of Osman). After that, Osman set his sights towards conquering the last of the Byzantine cities, towns, and fortresses in Anatolia. According to one account, after Sultan Alâeddin Kayqubad III was killed by the Mongols, viziers and notable leaders met and decided that since the late Sultan had no offspring, one of the local Emirs should take his place, and they found Osman perfect fitting the candidacy. Thus, the leaders offered the Emir the position, and Osman accepted becoming a Sultan. It is likely that Kayqubad's and Kaykāwūs's deaths led to the Sultanate of Rûm falling into chaos, and prompted many of its regular soldiers to join the armies of local Emirs, including Osman. This gave the latter a great momentum and important military experience enriching his army for the upcoming conquests.
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