There has never been a nation created based on the supposition that common genes are sufficient to build a government around. Most nations throughout history under all systems of government have ruled over regions which are mostly consanguineous, not just owing to the relatively low level of transportation technology available in the past. It’s also because people who are genetically similar tend to prefer the company of their fellows.
Knowing this, and knowing the errors of multiculturalism, it’s easy to proceed with just trying to argue one’s way back to an ethnic nationalism based mostly on common genetics. The most vulgar versions would be the American ideologies of black and white nationalism, which are both arguably rooted in prison culture. Prisoners separate themselves into ethnic factions because it’s a common denominator that can’t be faked.
When average Americans think of a ‘white nationalist,’ they think of a prison convert with swastika tattoos. They don’t think of the genteel, heroic Klansmen praised by Woodrow Wilson from Birth of a Nation — they think of the character played by Edward Norton in American History X.
In history, nationalism coincided with the decline of aristocracy and the rise of the nation-state. It was in opposition, often strongly so, even up to this day in nations like Spain, with governing ideologies related to ethnicity. Spain suppresses the Basques because the Basques assert their ethnic, regional identity against the national identity pushed down from Madrid.
France, Spain, the United Kingdom, Germany, and Russia are all patchworks of different ethnic groups with differing traditions and language dialects. Part of what made nationalism an unusual historical development was that it often involved the bulldozing of local ethnic cultures and their supplanting with new, national cultures.
That meant out with the local folk-story-teller and in with the national-great-novelist and national-composer and national-playwright and national-poet. You can’t just dispense with those people when you’re trying to ‘do the whole nationalism thing.’
It also coincided with a fair amount of ethno-religious in major and minor countries as the absolute monarchs struggled to consolidate their authority.
In the modern context, ethnic nationalism emerges amid ethnic conflict, driven by the state, in its attempts to further consolidate its own concept of nationalism. In France and the United States (along with other nations which mimic those countries), the nation-idea consists of a nationalism of the spirit, rather than one of the blood. People who affirm the national creeds of the French revolutionary state or the American revolutionary state as understood today, and go through the legal hoops, become labeled citizens, regardless of who they are and where they come from.
In this way, Barack Obama is a radical American nationalist, according to the tale told by the American nation-state which defines what it means to be such a nationalist. All of the propaganda published by the American state affirms that it is a multicultural nation which takes great pains to create a super-diverse state tolerant of all races and creeds.
It wasn’t always precisely so, but that’s the way that it is now.
Part of what’s generally positive among dissenting blood-and-genes nationalists of today is in recognizing that a nation formed on ever-mutating ideals is not a stable one, and a citizenship available to anyone with no standards (as Aristotle understood) is not a citizenship that is worth holding. No polis that refuses to maintain standards for citizenship can maintain cohesion for long.
So, while some measure of consanguinity is necessary to use nationalism as a political tool, it’s far from the only thing which is necessary.