[Excerpt] Throughout the ascendancy of mankind, migration has been among the most distinguishing behavioral characteristics of the human species. The noted historian William McNeill, in describing the pre-modern experience, has written that "it is safe to assume that when our ancestors first became fully human they were already migratory" because they were already hunters and, he adds, that "no dominant species ever spread so far so fast" as have human beings.1 From these early times until the modern era, there was little concern about how migrants might be received wherever they arrived. If the land area was unoccupied, the migrants simply settled it; if it was occupied, the newcomers might be absorbed if they came as individuals but, if they came in numbers, they often had to fight to displace those already there with the outcome of the struggle often being death, enslavement, or exile for the losers. Indeed, much of the recorded history of mankind is a story of repeated invasions of one people by another. Looked at from this long run perspective, all existing countries are "nations of immigrants". It is only a matter of the length of the time frame that is being examined.