The history of slavery spans many different cultures, tribes, nationalities and religions from ancient periods 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 has been found in some hunter-gatherer populations, particularly as hereditary slavery, but the conditions of agriculture with increasing social and economic complexity following the Neolithic Revolution which began in Western Asia circa 10,000 BC offer greater opportunity for mass chattel slavery. Slavery was institutionalized by the time the first civilizations emerged. Slavery features in the Mesopotamian Code of Hammurabi, which refers to it as an established institution. Slavery was widespread in the ancient world in Europe, Western Asia, the Indian subcontinent, Central Asia, East Asia, North Africa, West Africa, Central Africa, East Africa and the Americas.