> but I think a similar thing might happen if America broke up into separate countries. You’d still have a sizable amount of people that identify more as Americans than as Californians/New Yorkers/etc.

And yet, invariably when you meet an American in some other country, and ask him where is he from, he will answer "I'm from California/New York/Alabama/Ohio".

Back when I lived in Europe and had a lot of contact with international people, I used to pull the leg when that happened. If an American introduced himself like that, I will introduce myself in a similar way: "I am from Campeche" ... let HIM try to guess what that meant haha.