Bayezid attacks and defeats Karaman in 1391, annexes several Turkmen states in eastern Anatolia, and is preparing to complete his conquest in the area when he is forced to turn back to Europe to deal with a revolt of some of his Balkan vassals, encouraged and assisted by Hungary and Constantinople.

The sultan has meanwhile begun unifying Anatolia under his rule.

Forcible expansion into Muslim territories could endanger the Ottoman relationship with the gazis, who are an important source of warriors for this ruling house on the European frontier, so Bayezid has begun the practice to first secure fatwas, or legal rulings from Islamic scholars, justifying their wars against these Muslim states.

However, he suspects the loyalty of his Muslim Turkmen followers, for Bayezid relies heavily on his Serbian and Greek vassal troops to perform these conquests.

In a single campaign over the summer and fall of 1390, Bayezid conquers the beyliks of Aydin, …

…Saruhan and …

…Menteşe.

His major rival Sulayman, the emir of Karaman, responds by allying himself with the ruler of Sivas, Kadi Burhan al-Din and the remaining Turkish beyliks.

Nevertheless, …

…Bayezid pushes on and in the fall and winter of 1390 overwhelms the remaining beyliks—Hamid, …

…Teke, and …

…Germiyan.

...Niğde, as well as their capital ...

...Konya, from Karaman.

At this point, Bayezid accepts peace proposals from Karaman, concerned that further advances will antagonize his Turkmen followers and lead them to ally with Kadi Burhan al-Din.

Once peace had been made with Karaman, ...

...Bayezid moves north against Kastamonu, which had given refuge to many fleeing from his forces, and conquers that city as well as ...