CEVAP:

After the fall of the Anatolian Seljuk Sultanate , various Turk statelets were formed across Anatolia. One of these statelets was headed by Osman Beg at the northwest side of Anatolia bordering the remaining Byzantine lands surrounding its capital Constantinople. Osman Beg, and later his son Orhan Beg, took advantage of the weak position of the Byzantine state and enlarged their statelet by conquering almost all Byzantine land other than Constantinople (Istanbul) itself. Now a sizable state with a significant population and a loyal army getting ever stronger, the Ottomans were ready to expand both in Asia and Europe. One by one all the statelets in Anatolia fell to the Ottomans or pledged loyalty. The Ottoman Empire extended its territory and could not be stopped by the European countries.