Face the reality of history. Many cultures simply died out. Why couldn't the same happen here?

Another possibility is being bred into submission. This is what happened in China where over time the will to resist was culturally and genetically bred out of the population.

Those groups that survived in the face of oppression were those that were willing to move to save themselves. I am particularly thinking of Jews and Anabaptists. If you want your culture and your genes to survive, leave America and move somewhere where this will be possible.