I'm not sure that there are really any good historical parallels to what we are seeing in the West today; immigration on this scale was virtually unheard of before the 20th century. It's interesting to ask why rigorous border control is relatively new on the historical scene, and the only answer that jumps out at me is that the mass movement of people from the third world was never a problem because those people weren't doing it without someone to, ah, instigate them. There is something unique about the way that the world has picture-framed the American nation and the story of its formation; and it has been subject to more fictional-historical and ideological embellishment than any nation that I know of. It's like you have an entire globe and thousands of years of realism, and then this alien island called America that is supposed to break every trend in human history, and whose fictional example became the template for Europe. Some people might like to cite Rome as an example, but it isn't the same thing in my opinion. They were simply too sprawling of an empire to administrate, and their power kind of became this strange mobile abstraction called the Catholic Church. It's not so much that Rome died as it became a religious ethos that spread across Europe. I don't think there is an example in history where the dominant race/culture in a single nation was replaced through enforced immigration.