FWIW, the way I try and spin the issues are these:
- There are no "Vargr Raiders". They are opportunistic nation-states attempting to militaristically expand. Corridor had no cohesion and was picked apart piece by piece. Deneb retain political cohesion and was able to stave off the attacks.
- The Aslan had two independent efforts going on. One was the ihatei. The other were actual clan maneuvers. More below.
- The shadowed areas on the Spinward Marches map included with MegaTraveller show the deepest penetration of Vargr and Aslan incursions. None of the territory in the Spinward Marches was ever actually conquered by anyone.
- Norris' power play was done with the knowledge of others, if not all of the others. Anyone who might object was cowed by the threat of the vast majority of their peers. Delphine probably saw right through the whole charade, but didn't have the political backing to challenge it. Instead she wisely chose to back down.
For the Aslan, there were lots of things going on.
First, ihatei did quickly move into Imperial territory. No, they never "attacked" anyone. And they completely avoided any world with a reasonable population. They simply moved on low- and no-population worlds and squatted, knowing the Domain was busy dealing with other issues.
Second, this includes the "neutral zone" between the Domain and the Aslan. Quite simply, the Aslan just moved in an annexed it all. The Domain was too busy to even try and stop it, so they just moved in and took over. Actually, if you look at the world government codes for most of those worlds, they just pledged fealty to the Aslan and were left alone. It is only the low- and no-population worlds that get complete taken over and assimilated as "true" Aslan worlds.
Third, some of the clans tried to expand militarily. Some clans attack the Floriani, but, after some initial success, they stalled. Others quickly wiped out and absorbed the Glorious Empire. Still others tried to attack the Imperium while the first two groups were busy doing the first two attacks.
The result of all of this freaked out the Duke of Tobia. Seeing the Aslan on the move, and the Domain completely preoccupied with the (in his mind) irrelevant Zhodani, he brokered his own deal with the Aslan, resulting in much of the Domain territory in the Trojan Reaches "joining" the Aslan.
Of course, this deal was completely unnecessary, as the anti-Imperial clans were going to have to pull back quickly, since the other war efforts were winding down, and they couldn't afford to have their naval assets away from home, leaving their homes wide open for the other unoccupied clans that were still on a war footing. However, the Duke was pissed at Norris for ignoring him, and he just panicked. Not rational, but, hey, he was human, after all.
Once Norris realized the Zhodani weren't going to do anything, he started to get his house in order. He helped solify the coreward and trailing borders, but those had mostly taken care of themselves. The Vargr were only a threat if the defenders were disorganized. The Denebian defenders were organized and coordinated.
Norris then moved on down to deal with the Aslan. He was forced to skip over the various ihatei to deal with the real problem of Tobia. When his war fleets showed up at Tobia demanding that the Duke surrender himself for arrest, he blows his own brains out. A replacement is appointed, and the Trojan Reaches territories fall back in line. The Aslan can't do anything about the betrayal, except whine.
Finally, he starts to deal with the ihatei. But, by that point, Virus starts to show up, and he is forced to cut deals so he can deal with the larger issues.
That's my take. Still has holes you can drive a Tigress through, but hopefully it makes more sense than the default story.
