The new nationalism owes a lot to cultural factors, too. Many Westerners, particularly older ones, liked their countries as they were and never asked for the immigration that turned Europe more Muslim and America less white and Protestant. They object to their discomfort being dismissed as racism.
Elite liberals stress two sources of identity: being a good global citizen (who cares about climate change and sweatshops in Bangladesh) and belonging to an identity group that has nothing to do with the nation (Hispanic, gay, Buddhist, etc). Membership of certain identity groups can carry material as well as psychological benefits. Affirmative action of the sort practised in America gives even the richer members of the racial groups it favours advantages that are unavailable to the poorer members of unfavoured groups.
Nationalists dislike the balkanisation of their countries into identity groups, particularly when those groups are defined as virtuous only to the extent that they disagree with the nation’s previously dominant history. White Americans are starting to act as if they were themselves a minority pressure group.
Fear - Something very sick is at work when a country cannot endure a prolonged period of peace. Something is dreadfully wrong when a people cannot abide leaders...