[samstave]

Said "flags", typically, have the ability to tax, control, imprison and murder you either domestically or send you into a meat grinder in the name of "national security" etc..

So yeah, people tend to fall in line under a flag through a lifetime of indoctrination and threat of financial or physical violence...

[tiffanyg]

There's something more fundamental, though - humans are a "social species". Evolutionarily, we are adapted to requiring (generally) at least something of a group / tribe. Other organisms solve survival (of the species, ultimately) problems differently - incredible and 'cheap' reproductive capacity, strength and versatility enough to be much more solitary as a rule, etc. - those niches are somewhat to rather different.

In any case, at this point in human history especially, I'd argue it's time to consider "the group" to be ALL humans - "by default". There are nuances, and I'm out of time for commenting further right now, but, that's my take on it.

Hopefully, this comment is of some use to you / someone / etc. - hope y'all have a great day!