Mehmet the Conqueror can be named as the second founder of the Ottoman Empire. After the conquest of Istanbul he declared himself The Emperor of The Byzantine (Kaiser-i Rum) and established governmental institutes. First written construction was made by him and named as Kanunname-i Ali Osman (Laws of the Ottoman State). He gave his grand vizier authority to co-ordinate the divan (council). He began to observe the meetings of the council behind a curtain.

Mehmet the Conqueror moreover, classified the governmental duties and defined the ranks of the officers as defterdar(finance minister), kazasker (chef military judge). He established a central administrative system and organised a very powerful army.

He conquered the lands that had been lost in the reign of Yildirim Beyazid. With the capture of Crimea, Turkish sovereign in the Black Sea was proved. All the clans, principalities and states were unified in the Anatolia. The Turks had advanced through Belgrade.

In his reign many famous poets, scientists, philosophers came to Istanbul and Istanbul turned out to be the centre of arts and culture.