Men and women have been on the move since the earliest beginnings of human societies. Migration in small and large groups, and the establishment of new homes, have been among the strongest creative forces in the peopling and settling of the world's land mass and the making of human history. However, in the last two and a half centuries, far larger movements of population have occurred than ever before, changing the face of many local societies and of the planet itself. Among the most dramatic of these relatively modern flows of people have been those who travelled as slaves from Africa across the Atlantic, the Chinese who journeyed overseas as labourers and traders, the Europeans who migrated to northern America and to temperate climates in southern Africa, Australia and New Zealand, and the peoples of the Indian subcontinent who have spread out around the world in significant numbers. Such major flows of people have been propelled by demographic pressures, the forces of economics, and politics. Some have left home of their own free choice, whereas others have been compelled, whether formally or not. Some have been lured by hope, others driven by fear. For all of them, the technology of swifter travel has been a critical factor, as metalled roads and the internal combustion engine superseded human and equine feet as the fastest mode of travel on land, and as the sailing ship gave way to the steam ship in the nineteenth century, and eventually to mass air travel in the twentieth, to enable movement between continents and across oceans.