Comment by mosura

While a pan-US national awareness is widely seen as emerging during the civil war the rest of what you are saying is disingenuous. Prior to that it was a selection of colonies etc. which very much had borders because skirmishes over taxation rights was a thing.

There was significantly more inter ethnic strife in the US pre WW2 than most people seem to appreciate, much of it relating to if encountered (by whatever means) people should be settled/assimilated/rejected. There were riots/protests of this type in major cities at least between the civil war and the 1930s, and state policy reflected this, such as with the Chinese exclusion act which would hardly have been possible without a border.