Orhan also conquered the Turkish principality of Karesi in 1345-6, thus placing all potential crossing points to Europe in Ottoman hands. The experienced Karesi warriors were incorporated into the Ottoman military, and were a valuable asset in subsequent campaigns into the Balkans.

With the conquest of Karesi, nearly the whole of northwestern Anatolia was included in the Ottoman Beylik, and the four cities of Bursa, Nicomedia İzmit, Nicaea, İznik, and Pergamum (Bergama) had become strongholds of its power.

The acquisition of Karesi allowed the Ottomans to begin the conquest of European lands in Rumelia across the Dardanelles.