I think platoon is the right word, although I'm pretty terrible at army ranks and group sizes so don't take my word for it. I don't think there needs to be an army model per se - the extreme danger or the enforced closeness - but people do need a sense that they're working together to create that sense of unity out of diversity. Workplace dramas can have this dynamic too: they have the goal to hold them together, if not the danger.

And there are tons of stories about diverse groups of people pulling together after a natural disaster, say, to work together for survival. But that's short-term stress. I think long-term stress is often more corrosive?

Although in a case like India - the presence of the British was a long-term stress, but working against them was the goal that united disparate groups within India, and once that goal had been achieved there wasn't another shared purpose to draw people together. (Although of course there were lots of other factors: certain factions in the British government doing their darndest to foster disunity, for instance.)