The Mongol Empire, expanding westward under Ogedai Khan and then Batu Khan, saw Anatolia as a rich target. The Seljuk Sultanate of Rum, despite its cultural flourishing under rulers like Kayqubad I, was internally weakening at that time. A Mongol army, led by Baiju Noyan, decisively defeated the Seljuk army of Sultan Kaykhusraw II at the Battle of Kose Dag in 1243. This battle was a turning point. The Seljuks were forced to pay enormous amounts of tribute (taxes) in gold, silver, silk, animals, and other goods to their Mongol overlords. This crippled the Anatolian economy. Mongol governors and garrisons were stationed in Anatolia, ensuring compliance and extracting resources. They held the real power behind the weakened Seljuk throne.
The presence of Mongols in Anatolia fundamentally reshaped the political and social landscape of the region. The Mongol pressure further east pushed more Turkmen tribes westward into Anatolia. The Mongols heavily interfered in Seljuk succession disputes. They often appointed, deposed, and even executed sultans based on their loyalty and ability to pay tribute. This led to frequent civil wars among Seljuk princes vying for the throne with Mongol backing.
The Mongol invasion ended the golden age of the Seljuk Sultanate of Rum, turning it into a vassal state, specifically under the authority of the Ilkhanate (the Mongol division based in Persia) after the empire's fragmentation. While devastating in the short term due to economic exploitation and political instability, the Mongol domination inadvertently created the conditions for the rise of the Anatolian Beyliks by shattering central authority.
Mongol pressure and internal Seljuk weakness allowed local Turkmen tribal leaders (Beys) on the frontiers (especially the western frontier facing Byzantium) to assert increasing autonomy. These autonomous principalities are known as the Anatolian Beyliks. With the decline of Mongol influence in Anatolia, the Ilkhanate itself began to weaken due to internal strife and succession problems in the early 14th century, effectively collapsing around 1335. The Anatolian Beyliks seized this opportunity to become fully independent. They fought amongst themselves and against the remnants of Byzantine power. One of these Beyliks, founded in northwestern Anatolia by Osman I, was the Ottoman Beylik, which would eventually grow to conquer the others and establish the Ottoman Empire in 1299.