In the military, they have a saying: soldiers don’t fight for causes or countries, they fight for the guy next to them. Why would you die for the guy next to you?
It takes a very special kind of extremely cohesive grouping to sustain the kind of punishment that warfare dishes out. There is absolutely no reason to believe that members of a random group, without ties of kinship or race or shared political values for instance, would be willing to die for each other.
It turns out that what makes people willing to die for each other is actually the pressure of war itself. Facing death together means being reborn together. The metaphor of fire and forging is apt.
The cohesion has to be manufactured. The result is forged (as in metallurgy, not fraud) groups. How do you create forged groups?
You can take any logistically convenient, but otherwise random shared social variable, such as birth year or spatial collocation, and through sorting, grading and training operations, create a raw social unit that is functional on paper. But you won’t have any cohesion. But you do have something that can be forged, under the pressure of live fire, into a cohesive unit.
The result is something amazing: the forged group.
Military units are among the strongest anchors of social identity known to humanity. Soldiers fight primarily for the guy next to them because they share a forged-under-fire bond with him. They do not fight for their families, countries, emperors, generals, nations or abstract patriotic feelings because, valuable as those might be, they are far away.
Soldiers fight especially hard for units that are about as large as a paleolithic hunting party (between 15-30 members; this tends to be the size of the smallest effective military groups).
They fight hardest of all for units with which they’ve already shared hell-and-back experiences.
Every shared forging experience has the effect of making the group more socially homogeneous and therefore predictable. It is important to recognize that the homogeneity and predictability arises not from functional similarity among member roles, but emotional bonds forged among individuals by shared combat experiences.
Beyond forging, the metallurgical metaphors of tempering and annealing apply. The whole category of techniques known as heat treatment in fact. By using calculated thermal loading and unloading patterns, you can create very different properties in a metal. The same holds true for groups. Subjecting a group to an arduous 12-hour hike through the jungle is a different kind of heat treatment than making them fight an intense one-hour battle that tests their skills to the utmost.
There is a reason military units have mottoes and nicknames, expressing the collective identities forged in their first-blood experiences. These are expressions of unit-level combat doctrines. Extrinsic distinctions, such as fighter pilots versus bomber pilots, or infantry versus cavalry, only matter for unforged units.
It is possible to apply these ideas beyond the battlefield, but most people go about it in a naive way: offsite leadership retreats, ropes courses, and the much-satirized trust fall.
Real forging-by-fire in business happens through such experiences as launching a product together, being laid off together, banding together in a coalition to defeat a sociopathic executive, and so forth.
There is another reason forged groups are interesting: they can be treated as individuals for all practical purposes. The complexities of group dynamics don’t really enter into the picture. You can think in terms of group archetypes, doctrines and narratives.