Life is funny sometimes in that by insisting that something is, you make that insistence a reality. While I can certainly agree that it's not healthy for the north, a couple thoughts. Eponllyn is not going to be encouraged to depart from any of those alliances by constantly being compelled to rely upon them. The alliances are also self-harm to their own realms because there are no nearby enemies and the allies are too far away. For the same reasons the Southern League/Astroist Federation suffered against Luria that any Nivemus/Sirion/Eponllyn alliance would suffer against Perdan/Vix.
In terms of worry, the alliance is a paper tiger. It's not my ideal state of affairs. I look forward to more diverse diplomacies up north. It won't change overnight though just because we want it to. Eponllyn has tried to pursue new policies, but Perdan and Vix have chosen for more of the same old alliances that have dominated EC history. I do not mean that negatively as you describe the sirionite alliances, just descriptively in that to me, it looks very much like Vix/Perdan have chosen their shared history/culture over innovative diplomatic relations that very well might have reduced the alliance-chain you are now so worried about. Eponllyn wasn't alone either. Nivemus was pursuing independent policies under Catherine of a pro-Perleone/anti-Perdan nature that might have driven Nivemus and Eponllyn further apart on account of Eponllyn's (at the time) budding friendship/alliance with Perdan and hate of Perleone.
I agree mostly with Vita especially the last part about Catherine who is the last Ruler of Nivemus before Brock. Under her grace, Nivemus is working to move far from the north alliance, towards helping Perleone. After all, why would Nivemus army came so far down south just to assist Perleone in their war against Perdan however futile it looked?
Unfortunately this current war titled above, have only brought all the allies together(that grew some distance apart after that last big war in the north). Some of your characters may state that you wish to break apart Sirion alliance, but in fact, without offering any other viable alternative(in allies or diplomacy or other treaty good terms), all the so-called northern alliance will only stand together. Eponllyn already chose to help the smaller realm such as DSS realm by stopping other bigger realms from using their lands to attack DSS or Sirion), Eponllyn appears to be moving on this new direction right until this war titled above crops up
You obviously haven't seen the current state of Sirion. Or Eponllyn. Or know much at all about the current political state of the island. Or anything about the military status of the various realms. I mean, really. That statement smacks of a blatant "I looked at the diplomatic standings chart and realm list, and drew a completely unsupportable conclusion". The idea that the northern alliance block is a threat to anything is ludicrous.
I see that and have a lot of data on my hand. It is sad though. If only 1 realm(either Vix or Perdan) fought with Eponllyn, Eponllyn should have no problem holding their own. After all, the data I have(number of nobles who capable of recruiting units size) show each realm have almost same number of characters. Vix and Perdan both combined of course have more nobles than Eponllyn.
Even Nivemus is also growing weaker nowadays, judging from the army it sent down south to assist Eponllyn as you all may noticed. We do not have enough noble to fill our regions lordship, my character Ruler of Nivemus has to juggle General responsibility as noone interested to take it up.
In short, the north alliance is as paper tiger as it can get. Without number of nobility to fill in the ranks and attracting nobles, it is only a matter of time.
I'm sure Fontan agrees with you.
Wait a minute. My character is former Fontan noble. He wants recreate Fontan deep inside his heart. But now he is Nivemus Ruler