Rise of the Ottoman Empire
The foundation and rise of the Ottoman Empire is a period of history that started with the emergence of the Ottoman principality in , and ended with the conquest of Constantinople on May 29, 1453. This period witnessed the foundation of a political entity ruled by the Ottoman Dynasty in the northwestern Anatolian region of Bithynia, and its transformation from a small principality on the Byzantine frontier into an empire spanning the Balkans and Anatolia. For this reason, this period in the empire's history has been described as the Proto-Imperial Era. Throughout most of this period, the Ottomans were merely one of many competing states in the region, and relied upon the support of local warlords and vassals to maintain control over their realm. By the middle of the fifteenth century the Ottoman sultans were able to accumulate enough personal power and authority to establish a centralized imperial state, a process which was brought to fruition by Sultan Mehmed II (r. 1451-1481). The conquest of Constantinople in 1453 is seen as the symbolic moment when the emerging Ottoman state shifted from a mere principality into an empire, marking a major turning point in its history.
Ottoman Empire
As the Seljuk Sultanate of Rum declined in the 13th century, Anatolia was divided into a patchwork of independent Turkish principalities known as the Anatolian Beyliks. One of these beyliks, in the region of Bithynia on the frontier of the Byzantine Empire, was led by the Turkish tribal leader Osman I (d. 1323/4), a figure of obscure origins from whom the name Ottoman is derived. Osman's early followers consisted both of Turkish tribal groups and Byzantine renegades, many but not all converts to Islam. Osman extended the control of his principality by conquering Byzantine towns along the Sakarya River. It is not well understood how the early Ottomans came to dominate their neighbours, due to the lack of sources surviving from this period. The Gaza Thesis theory popular during the twentieth century credited their success to their rallying of religious warriors to fight for them in the name of Islam, but it is now highly criticised and no longer generally accepted by historians, and no consensus on the nature of the early Ottoman state's expansion has replaced it.