I would suggest to get confirmation if the Defense pact actually triggers if a TAMDA member goes into war and then gets counterattacked or if it always counts at the time a TAMDA fief or party within Tundra gets attacked.
The war between those parties is going on for a while now, so claiming now that the Defense Pact is being triggered without a fief getting attacked which was in the claims of those TAMDA members at the time the treaty was made is a bit thin.
I see where you're coming from, and I believe I asked a similar question before joining TAMDA. The way I understand it is that if war should enter the Tundra, the factions would sanction together to keep it from spreading and attempt to contain it, if not all together extinguish it. Given the circumstances that HG is apart of Remnant Faction, they somewhat inherit their Father's war, and given that Remnant has made it clear they aren't apart of TAMDA, yet HG is, it leaves me scratching my head as well.
It would be easier for HG if they separated from Remnant Faction and created their own, they're big enough to do so now, and hopefully active enough. But I think that's what's happening here, inherently getting attacked based on Faction association, not so much the clan itself. And thus, if that's the case, does TAMDA in fact cover it since it's not so much an attack directed to HG, as it is directed at Remnant?
Food for thought.