The industrial development of ancient civilisations was largely based on Slavery, and, from the earliest periods of which history has any record, countries lying within the tropics — always prolific Of population — were raided to supply the slave-markets of the world. It was thought worth while in the great days of Egypt, Persia, Greece, Rome, and mediaeval Spain, to be at the expense of sending caravans into the Soudan for slaves, who had to be hunted and caught in the tropical regions further south. Notwithstanding the cost of the overland journey, the expense and waste of slave-hunting, and the large percentage of deaths which occurred in transit, the labour of Africa was considered valuable enough to be worth transporting to any market in which it was required. The trade was continued through the Middle Ages, and under modern conditions of steam shipping and travelling it was still found worth while less than fifty years ago to carry African labour to America. We have abolished slavery, and, as a consequence, it has been assumed that the labour which once supplied the great industries of the world has ceased to have any value.