how simple is it , the "genetic purity" is the problem in America ! please feel free to elaborate , THANKS
I'm not quite sure what you're asking here; but since you mention "genetic purity" and America, I'll say a bit about these topics.
Genetic purity, in my views, is necessarily a relative thing. I'm not a "one-dropper" - one of those who say if you have a single non-White ancestor twenty generations back, you don't qualify as White. Instead I see some degree of race-mixing as inevitable in the meanderings of historical events. Some people may have willingly miscegenated out of ignorance or apathy; some may have been subject to rape.
I settle for Robert J. Mathews' criteria: If someone looks White, acts White, and identifies as White, then until some compelling evidence to the contrary is produced, they are White. This can be used in concert with the five second rule: If you can't decide whether someone is White within five seconds of looking at them, they are not White.
I once made a list of the races in an order rating them from most harmful to least harmful to be mixed with. Jews and Blacks were at the bottom of the list as most harmful; at the top of the list as least harmful were American Aboriginals. One fellow responded to my list with the complaint that, if he had to be mixed, he'd rather it be Japanese or Chinese than Aboriginal (Japanese and Chinese falling somewhere in the middle of that list). I replied that he was prejudiced by the fact that those Asian races exhibited a higher degree of advanced civilization than the Aboriginals, and that this was not the criteria to adhere to: those Asian races are more genetically removed from, more alien to, us than are the Aboriginals. Aboriginals are less harmful to mix with because they are genetically closer to us than the other Asian races, even though their ancestry originates in Mongolia.
Some European White nationalists sneer at North American White nationalists because they see us as hopelessly mongrelized - not necessarily with non-Whites, but with divergent White racial sub-groups and ethnicities, to a degree where they feel it alienates us from our essential European roots. Say if someone were half Irish and half German, or half Italian and half Russian; these are all White European groups, but a mixed White would be conflicted as to their essential original heritage.
Others, both in Europe and America, disagree, seeing that even Whites from multiple European backgrounds still bear the qualities necessary to build and maintain an advanced civilization.