Tribal is my best guess at his meaning, but ingroup is related, or perhaps partisanship when applied to American politics. Nationalism feels incorrect, especially when he chooses examples of beliefs that are against their own nation (skip to the heading “negative nationalism”), or examples that are not much to do with nationality (political Catholicism, Antisemitism, Pacifism).

Another theme is blind loyalty (authority figures) versus freethinking. As a geek I try to avoid succumbing to geek groupthink, although HN doesn’t always help that goal.