The Aslan "Moment of Clarity" came as they avoided extinction by nuclear holocaust and developed their jump drive. The Moment ended fairly quickly once their homeworld was no longer under threat of nuclear reset, but the return to low level warfare with occasional open conflict began as they were vying for control of other systems. Spreading into human Long Night space was bloody, and not just between humans and Aslan.
The Heirate presents itself much like Japan did: culturally unified in all important ways. A veneer of family and Clan specific tradition is certainly present, but they all subscribe to the core values. Whether those are coming from a genetic base or have been imposed through positive AND negative reinforcement in the 2000+ years they've been spacefaring is another matter. The Heirate Ihatei made certain that the Glorious Empire died and was reabsorbed for what most outsiders would consider minor variations from Heirate cultural norms.
That's not to say that Aslan are all the same. There is, by most accounts, still a significant Aslan population in Imperial space, concentrated largely in Daibei. Much like the Vargr in Imperial space, they've adapted. Only the cultural traits driven by genetics are universal amongst those populations; Aslan males feel the drive to own land in their bones, and Vargr siblings and adult "packs" still practice internal stratification via the mechanisms of Charisma. Everything else is subject to adaption.
The patterns across the map of Charted Space are pretty clear, though: Races that have had major division/isolation events tend to be more culturally diverse than those which have been secure and unified for their entire spacefaring existence. This pattern is one of the things that gives the dual whammy of Virus and the Wave so much potential; together they are the population bottleneck at many local levels and the isolation of survivors from each other that lead to rapid cultural drift. Two Major Human races have done this before, and it shows. The Virus and Wave impose it on everyone else.
That's interesting. I vaguely recall the nuclear standoff, but I can't remember which supp I read it in. MT or GT.
But other than their pre-space bound homeworld grudge matches, I don't recall a history of warfare of clans squabbleing over colonizable super Earths or Mars like worlds. I think either GT or MT supps might have implied that kind of history, but unlike the Soli and Vilani clashes and civil wars, I've not read anything about clans butting heads. It would make for an interesting supp for the die hard "must have everything" Traveller fan.