The history of slavery spans many cultures, nationalities, and religions from ancient times to the present day. Likewise, its victims have come from many different ethnicities and religious groups. The social, economic, and legal positions of slaves have differed vastly in different systems of slavery in different times and places.Slavery occurs relatively rarely among hunter-gatherer populations because it develops under conditions of social stratification. Slavery operated in the first civilizations (such as Sumer in Mesopotamia, which dates back as far as 3500 BC). Slavery features in the Mesopotamian Code of Hammurabi (c. 1860 BCE), which refers to it as an established institution. Slavery was widespread in the ancient world. It was found in almost every ancient civilization, including the Roman Empire. It became less common throughout Europe during the Early Middle Ages, although it continued to be practiced in some areas. Both Christians and Muslims captured each other as slaves during centuries of warfare in the Mediterranean. Islamic slavery encompassed mainly Western and Central Asia, Northern and Eastern Africa, India, and Europe from the 7th to the 20th century. The Dutch, French, Spanish, Portuguese, British and a number of West African kingdoms played a prominent role in the Atlantic slave trade, especially after 1600. Although slavery is no longer legal anywhere in the world, human trafficking remains an international problem and an estimated 25-40 million people were enslaved as of 2013, the majority in Asia. During the 1983–2005 Second Sudanese Civil War people were taken into slavery. Evidence emerged in the late 1990s of systematic child-slavery and trafficking on cacao plantations in West Africa.Slavery in the 21st century continues and generates $150 billion in annual profits; modern transportation has made human trafficking easier. Regions with armed conflict have vulnerable populations. In 2019 there were an estimated 40 million people worldwide subject to some form of slavery, 25% of them children. 61% are used for forced labor, mostly in the private sector. 38% live in forced marriages. Other types of modern slavery are child soldiers, sex trafficking, and sexual slavery.