Immigration by consent is just as dangerous as armed conquest.
Two interesting maps which show how quickly (historically) a native people can lose their land. Now, via these maps, you can see how quickly a neighborhood or a town or even a country (never mind half a continent!) can be infiltrated and overturned by hostile culturally dissimilar people. Places like London, Birmingham, Paris, Berlin, and much of the white West show a similar pattern. Pass it on.
http://www.europeanamericansunited.org/home/node/9