Humans had always been migrating. Many years ago, our ancestors left the shores of Africa and braved harsh weather and other perils to colonize the entire world. Then, in the intervening centuries they largely took to agriculture and settled down in their towns and hamlets. These were self-contained economies, rarely requiring anybody to venture out anywhere else. However, later, large scale migrations from the villages to the cities started with the onset of industrialization, and modern-day globalization has accelerated the pace of this movement.