Slavery in the Ottoman Empire was a legal and significant part of the Ottoman Empire's economy and traditional society. The main sources of slaves were wars and politically organized enslavement expeditions in North and East Africa, Eastern Europe, the Balkans, and the Caucasus. It has been reported that the selling price of slaves decreased after large military operations. In Constantinople (present-day Istanbul), the administrative and political center of the Ottoman Empire, about a fifth of the 16th- and 17th-century population consisted of slaves. Customs statistics of these centuries suggest that Istanbul's additional slave imports from the Black Sea may have totaled around 2.5 million from 1453 to 1700.