After hearing a recent conversation in which some sort of metric for unity was implied, I have begun to wonder what exactly what that metric could be. I don't think the people actually having the conversation knew what the metric was either. They were just analyzing events with a veiw to whether they increased unity, which in the end comes down to whether or not the event made one feel that warm and fuzzy feeling of unity. Which, in and of itself is okay, but I doubt it really works as a good metric.
Now, if your descendants and my descendants happen to be the same people, that would correlate highly (after the fact) with our unity. Unfortunately, as any child of divorce can tell you, it doesn't correlate perfectly, nor does it provide any sort of predictive content that so many people like in their indicators.
The very question can be answered on so many scales- in some cases the unity expressed would be practically superficial. If for example, people were actively negating their identities for the group, then it becomes a sort of faux unity because we don't really ever get to know one another. We, as humans also have an upper limit for how many other humans we can actually have a relationship with. To attempt more than that means all relationships suffer, and that would ruin any perceived unity too.
The examples above, you'll note, are about the level of unity within a group that purports to be unified, or claims unity as one of it's desires. Obviously, people who are in open warfare with one another aren't unified, but then one doesn't need a metric of unity to figure that out. Who have you had dinner with lately helps at a certain level. Ultimately this will come back to maintaining relationships, which we have to do on a personal level. So, in the end, attempting to encourage unity through group identity reinforcing activities is probably contraindicated, because the time would be better spent with people strengthening the personal relationships that drew them (and keep them) in the group in the first place.