Another reason why the federal system would be necessary

A continuation of this post.

If a people define themselves not just by a common lineage or genealogy and a common land, but also by a shared culture, then if the United States is composed of different cultures owing to the different origins of the first Anglo (and European) settlers who came here, should we not say that there are many American peoples, rather than a single American people? (Assuming that these differences have been maintained up to the present-day.) And if this is the case, and each culture has its own specific customs, should there be a single, central government ruling them all? Or should not each people be self-governing as much as possible, uniting if they wish, under some sort of federal government? (Rather than a centralized unitary national government?) While some laws governing trade between each people could be agreed upon at the federal level, how could the federal government be competent to decide upon more particular laws that would apply to all the peoples, if they have disparate customs settling the fundamental questions of justice?

(I ask the question about people and not of states to serve as a reminder that we need to come to a more clear understanding of how a people define themselvse [its self?].)