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).
Territorial evolution of the Ottoman Empire
Selim carried the empire to the leadership of the Sunni branch of Islam by his conquest of the Middle East. He represents a sudden change in the expansion policy of the empire, which was working mostly against the West and the Beyliks before his reign. On the eve of his death in 1520, the Ottoman empire spanned almost (trebling during Selim's reign). These included few dependent, vassal states as like Walachia from 1396, Crimea Khanate from 1475, Moldavia from 1501
and Algeria from 1520.