You can’t have a nation of tribes. You have one or the other. And that’s largely defined by the extent to which reproduction is endogamous vs. exogamous. I mean, you could have a confederation of tribes or something, but it would be a totally different arrangement than a homogenous nation, for which it might make sense to think or speak about nationalism. You would have concentric loyalties and ingroup, rather than shared ones.
Tribalism is based on direct, usually known, kinship. Nationalism is based on more distant kinship, the exact degree of which need not be known. Same basic concept, but at a different scale. Nations are bigger than tribes, yet still practice ingroup trust and ingroup altruism.
The reason Europe has nations though much of it was once, rather recently, occupied by tribes, is that Roman law prohibiting inbreeding within 4 degrees of separation measured to the common ancestor and back, was superceded by church canon Law from the 9th to the 12th centuries which prohibited inbreeding within 7 generations, measured to the common ancestor, but not back. That’s what destroyed tribalism in Europe, and created homogenous outbred nations, except for a few holdouts on the fringes (e.g. Scotland.)
While nationalism offers some advantages over tribalism, large, efficient, trustworthy markets and institutions, things of that sort; trying to take things further, to internationalism, is dubious on a number of grounds.
First, the maintenance of ingroup trust and ingroup altruism is doubtful since enforcement of reciprocity becomes more difficult and costly at scale and in proportion to differences; and even more so since internationalist ideologies prohibit insistence on reciprocity. Non reciprocity is parasitism and parasitism is costly.
Second, it’s not clear that homogeneity *between* nations, as opposed to within them, offers any advantages. Though large, nations can still adapt to local conditions and adopt a variety of different coherent strategies and trade-offs, which may confer different advantages for different circumstances, or allow them to fill different niches. International homogeneity would tend to erase those distinctions and that coherence and replace it with randomness; followed, perhaps eventually, by a new sameness that does not allow for optimal exploitation of local opportunities and conditions, nor build on past adaptations to the same.
But if nationalism gives way to internationalism, then internationalism will inevitably give way, once more, to tribalism, since an internationalism which does not demand reciprocity is not competitive against non-reciprocal, parasitic, strategies.
And that’s the path we’re going to have to take, if we can’t salvage nationalism.