section_path: Characteristics/Economics
section_name: Economics
paragraph_text: Economics
  
  Economists have modeled the circumstances under which slavery (and variants such as serfdom) appear and disappear. One observation is that slavery becomes more desirable for landowners where land is abundant, but labour is scarce, such that rent is depressed and paid workers can demand high wages. If the opposite holds true, then it is more costly for landowners to guard the slaves than to employ paid workers who can demand only low wages because of the degree of competition. Thus, first slavery and then serfdom gradually decreased in Europe as the population grew. They were reintroduced in the Americas and in Russia as large areas of land with few inhabitants became available.
  
  Slavery is more common when the tasks are relatively simple and thus easy to supervise, such as large-scale monocrops such as sugarcane and cotton, in which output depended on economies of scale. This enables systems of labour, such as the gang system in the United States, to become prominent on large plantations where field hands toiled with factory-like precision. Then, each work gang was based on an internal division of labour that assigned every member of the gang to a task and made each worker's performance dependent on the actions of the others. The slaves chopped out the weeds that surrounded the cotton plants as well as excess sprouts. Plow gangs followed behind, stirring the soil near the plants and tossing it back around the plants. Thus, the gang system worked like an assembly line.
  
  Since the 18th century, critics have argued that slavery hinders technological advancement because the focus is on increasing the number of slaves doing simple tasks rather than upgrading their efficiency. For example, it is sometimes argued that, because of this narrow focus, technology in Greece – and later in Rome – was not applied to ease physical labour or improve manufacturing.
  
  Scottish economist Adam Smith stated that free labour was economically better than slave labour, and that it was nearly impossible to end slavery in a free, democratic, or republican form of government since many of its legislators or political figures were slave owners and would not punish themselves. He further stated that slaves would be better able to gain their freedom under centralized government, or a central authority like a king or church. Similar arguments appeared later in the works of Auguste Comte, especially given Smith's belief in the separation of powers, or what Comte called the "separation of the spiritual and the temporal" during the Middle Ages and the end of slavery, and Smith's criticism of masters, past and present. As Smith stated in the Lectures on Jurisprudence, "The great power of the clergy thus concurring with that of the king set the slaves at liberty. But it was absolutely necessary both that the authority of the king and of the clergy should be great. Where ever any one of these was wanting, slavery still continues..."
  
  Even after slavery became a criminal offense, slave owners could get high returns. According to researcher Siddharth Kara, the profits generated worldwide by all forms of slavery in 2007 were $91.2 billion. That was second only to drug trafficking, in terms of global criminal enterprises. At the time the weighted average global sales price of a slave was estimated to be approximately $340, with a high of $1,895 for the average trafficked sex slave, and a low of $40 to $50 for debt bondage slaves in part of Asia and Africa. The weighted average annual profits generated by a slave in 2007 was $3,175, with a low of an average $950 for bonded labour and $29,210 for a trafficked sex slave. Approximately 40% of slave profits each year were generated by trafficked sex slaves, representing slightly more than 4% of the world's 29 million slaves.