“They traveled deep into far-flung regions of their own country and in some cases clear across the continent. Thus the Great Migration had more in common with the vast movements of refugees from famine, war, and genocide in other parts of the world, where oppressed people, whether fleeing twenty-first-century Darfur or nineteenth-century Ireland, go great distances, journey across rivers, desserts, and oceans or as far as it takes to reach safety with the hope that life will be better wherever they land.”