Very soon, however, the ordinary sources of supply of slaves was not sufficient to meet the demand of the American trade. Then traders became less scrupulous. They began buying from any one who had a man or woman for sale. This encouraged kidnapping. Not infrequently the man who brought a gang of slaves to the coast to be sold would himself be kidnapped and sold by other men before he could return home. Sometimes the traders, after they had purchased a gang or a "coffle" of slaves, as they were called, would invite the traders on board ship in order to entertain them. Then, after they were under the influence of liquor, they would put chains upon them and carry them away with the very slaves the traders themselves a few hours before had sold. As time went on, and the demand for slave labor increased, the men engaged in this cruel traffic became hardened to its cruelty and the West Coast of Africa became one vast hunting ground. Men and women were tracked and hunted as if they were wild beasts. It grew so bad at length that the conscience of the civilized world was aroused. Then, one by one, the nations of the world began to prohibit the traffic. England, which had formerly been one of the nations most deeply involved in this evil business, now became the leader in the attempt to put a stop to it. The importation of slaves was prohibited in the United States in 1808, but that did not put an end to the importation of slaves. For, after the invention of the cotton gin at the close of the eighteenth century by Eli Whitney, a Connecticut school master, slaves were needed more than ever, to plant and till and pick the cotton which had now become much more valuable than before. Although it was no longer lawful to import slaves, they were smuggled into the country. As late as 1860 the famous yacht, Wanderer, which had at one time been owned by a member of the New York Yacht Club, brought into the United States 450 slaves, and it has been estimated that as many as 15,000 slaves were smuggled into the different Southern ports in the year 1858. At this time it had become the custom to gather great numbers of slaves at different points along the coast of Africa, in what were called barracoons. These were nothing more or less than strong stockades made by planting trees close together in the ground so as to form a strong enclosure from which there was no escape. In these barracoons slaves captured in the interior were held until they were ready to be shipped. Swift sailing vessels, which travelled so fast that, once they escaped the vigilance of the war ships stationed along the coast, they could never be overtaken, were used to carry the slaves from the coast of Africa to that of America.