Why were the ottomans so successful at expanding and unifying their empire?

Pressured out of their homes in the Asian steppes by the Mongols, the Turkish nomadic tribes converted to Islam during the eighth and ninth centuries. By the tenth century, one of the Turkish tribes, the Seljuk, had become a significant power in the Islamic world and had adopted a settled life that included Islamic orthodoxy, a central administration, and taxation. However, many other Turkish groups remained nomadic and, pursuing the gazi tradition, sought to conquer land for Islam and to acquire war booty for themselves. This led them into conflict with the Seljuk Turks, and to pacify the nomadic tribes, the Seljuks directed them to the eastern domain of the Byzantine Empire, Anatolia. The tribe known as the Ottomans arose from one of the smaller emirates established in northwestern Anatolia after 1071. The dynasty was named for Osman (1259-1326), who began to expand his kingdom into the Byzantine Empire in Asia Minor, moving his capital to Bursa in 1326.

He gathered information from primary sources.