The he history of human civilisation has time and again witnessed collective migrations driven by political upheavals, dictatorial coercions, home wars, economic depressions or natural calamities like epidemics, floods or earthquakes. The oldest such example in history is perhaps the exodus of the Jews led by Moses, And Moses said, we will go with our young and with our old, with our sons and with our daughters, with our flocks and with our herds, will we go.... This arduous journey happened by defeating the pursuing horsemen of the Pharaoh of Egypt, and by crossing the bifurcated Red Sea. It is signified in human history as the journey of liberation.\r\n

Another devastating migration took place in Ireland in the nineteenth century not because of political suppression but due to the damage of harvest by natural calamity. Between 1845 and 1851, ten lakh people died in Ireland because of the potato epidemic. As a result, millions of people abandoned their home and hearth. While the population in 1851 was around 80-85 lakhs, in a decade it came down to sixty-five lakhs. Loss of harvest, famine and epidemic forced regular migration so much that by 1921 the population of the country had been reduced to only forty-three lakhs.