Segregation, as I use the word, has nothing to do with walls. It is the uneven allocation of attention and attachment across group lines — a definition built to travel. It covers citizens’ private information worlds; it covers publics turning against other nations and the leaders who speak for them; it covers expert communities that sort by nationality and legislatures dividing over technology. One concept, several altitudes.
The faces it takes are worth keeping separate, and each has its own note: attention — what holds people; affect — how hot the division runs; identity & ideology — which lines it runs along. And measuring any of them honestly is a problem of its own: measurement & validity.