Decline and modernization of the Ottoman Empire
Beginning from the late eighteenth century, the Ottoman Empire faced challenges defending itself against foreign invasion and occupation. In response to foreign threats, the empire initiated a period of tremendous internal reform which came to be known as the Tanzimat, which succeeded in significantly strengthening the Ottoman central state, despite the empire's precarious international position. Over the course of the nineteenth century, the Ottoman state became increasingly powerful and rationalized, exercising a greater degree of influence over its population than in any previous era. The process of reform and modernization in the empire began with the declaration of the Nizam-ı Cedid (New Order) during the reign of Sultan Selim III and was punctuated by several reform decrees, such as the Hatt-ı Şerif of Gülhane in 1839 and the Hatt-ı Hümayun in 1856. At the end of this period, marked with 1908, to a degree the Ottoman military became modernized and professionalized according to the model of Western European Armies. The period was followed by the defeat and dissolution of the Ottoman Empire (1908–1922).
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.