Tribes predate nation states by several hundred thousand years.

The modern nation state is a fairly recent invention. But to the point, yes, seems to me it only ever worked because people felt as a tribe under its banner, along with shared values, ways of seeing the world, common goals, etc.

Most of that seems to go away when multiple tribes from incompatible places each with competing values are artificially put together under that same single banner.

If at least it's organic and the rate is throttled and the newcomers are vetoed (coming to add value and not to leech, compatible cultural values etc) then it's probably find. But gazillions unvettoed coming to overload an already fragile system, from cultures with incompatible values, who largely have no wish to integrate with the broader culture, then yeah.. different story.