Historically, each early human had one tribe. One tribe of say 80 people, but far from placidly peaceful: Each early tribe was (often) a cauldron bubbling hot with factions & shifting allegiances on various decisions.
Early humans rarely switched tribes, moved from one group of 80 to another. Maybe one of every four people switched tribes even once in a lifetime, and always with a great deal of drama and difficulty. Worse, being cut off altogether from one's original tribe -- and never fully feeling at home in a new one -- was probably more common than true tribe-switching.
I sense that we each have a feelingspace for some true tribe -- real or imagined. As a modern civilized adult, I sense it mainly in 3 places: 1) family (early environ household, etc), 2) closest companions & friends & fellow travelers in the microculture(s) you feel most at home in, 3) idealized imaginary audiences/judges/observers. The third's structure is the least easily directly perceptible, but it is usually the most powerful re: big personal decisions at least in Western culture. The phrase "American Cowboy" is almost entirely about that third: Clint Eastwood's usual type, Bruce Willis in Die Hard, Arnahd when he's playing anything other than a killer robot... [I would have written "anyone" instead of "anything", but Arnold comes off more like a force of nature!]
Those "3 places" diverge much more in modern civilization than back in the day. This adds new layers of anxiety & uncertainty on to our experience. The 3 places' divergence/tension is uncomfortable -- loyalty sure ain't as clear it used to be, and it used to be about as complex as our brains evolved to handle!
In some ways, we moderns resolve that divergence/tension by splitting our lives -- time & energy -- into clean pieces of a pie that each competing tribal sense gets to pretty much hoard to itself. As a huge example, almost all moderns direct almost all of their money -- & related fruits of achievement -- ultimately to tribal sense #1 (family). This is so powerfully pervasive that we almost don't notice it -- it's just "obvious" to us, though it's far from the only way culture could have evolved.
Sense #2 (closest companions & friends & fellow travelers) is really interesting intergenerationally right now. I've learned a lot about it by attending some Old People parties this year! (Both my older-generation extended family, and Farsam's.) The older generations today base Sense #2 on much more superficial&accidental commonalities than we tend to. Youthful globe-trotting intellectuals are very picky compared to the oldsters, who are many times "merely" about who's still alive & remembers the small town they grew up in.
Alienation is the feeling of being apart from -- away from, cut off from, or totally useless to -- one's tribe. Modern civilization causes a lot of alienation by splitting one's most socially useful work from one's true senses of tribe. (Corporate environs ameliorate this by creating secondary tribes -- but they make us feel almost treacherous to our core tribes in the process. See "...still Jenny from the block..." or whatever!)
All that focused on your true senses of tribe -- which are generally stable over many years. In modern societies, we can see those stable internal senses interacting with outside swirling immediate social environs of all kinds. I often research & write in an urban hipster part of town -- and I watch people's body language & seating selection announce which other folks whose opinions they're choosing to let matter (which is my basic definition of "tribe", remember). As an automatic part of wandering through swirling social environs, we each constantly compile & compare all the perceptible details of those around us -- organized by how similar they are to our various tribal ideals! (We also carry around particular anti-tribe, enemy tribe, templates -- unless we're very effectively self-policing (post)modern liberal academic types!) This explains racism, a lot of lookism, and your best job interview ever.
(Post)modern liberal academic youthful globe-trotting intellectuals (PLAYGI) are pretty much the only thoroughgoing tribe-deniers in world history. Ayn Rand was one of the first total tribe-deniers -- but only at a conscious verbal level. In reality, she loved Russian Jews who'd expatriated to North America & to Objecticorrectness!! I've met plenty of PLAYGI who are much more deeply integratedly tribe-denying than Rand was, and it can be a beautiful thing.
With the actual human hardware (bodyminds!) we've inherited, we can never be truly trans-tribal. However, we could get extreme PLAYGI effects by pushing all noticeable true senses of tribe farther toward the infamous Dr. Bronner's famous "ALL ONE!!!"
My current judgment is that today's median PLAYGI pushes the tribal senses about as far as they should (healthily) be pushed in today's world. It's plenty dangerous to have an overinclusive sense of tribe -- at least when so many other people do not!