Slavery is a system under which people are treated as property to be bought and sold, and are forced to work. Slaves can be held against their will from the time of their capture, purchase or birth, and deprived of the right to leave, to refuse to work, or to demand compensation. Slavery began in prehistoric times and has been practiced ever since. The slavery of ancient times reached its peak in Greece and the Roman Empire. During the middle Ages, slavery declined. Then, during the 1500's and 1600's, the colonization of the New World by Europeans resulted in a great expansion of slavery. Changing moral attitudes about slavery helped cause its decline during the 1800's. The United States abolished slavery in 1865. Today, slavery is illegal in almost every country in the world. But slavery still exists in parts of Africa, Asia, and South America. Congress, using powers granted by Article I, Section 9, of the Constitution banned importation of slaves in 1808 but this did not affect those already in the United States or those yet to be born. Slavery has a number of subcategories; these include Bride-buying, Child labor, Debt bondage, human trafficking, Sexual slavery, Sweatshop and Wage slavery. The start of slavery probably followed the development of farming about 10,000 years ago. Farming gave people an opportunity to put their prisoners of war to work for them. People captured in war continued to be the chief source of slaves in the earliest civilizations. Other slaves were criminals or people who could not pay their debts. The first known slaves formed the lowest class in the civilization developed by the Sumerians in Mesopotamia about 3500 B.C. Slavery also existed in Assyria, Babylonia, Egypt, Persia, and other ancient societies of the Middle East. In addition, it was practiced in ancient China and India and among the early blacks of Africa and the Indians of America. Slavery expanded as commerce and industry...