So here's how Melhed could've (IMHO) won the war. This strategy would've had to have been executed from the beginning, when the fundamentals where more similar. We'll assume that both realms have 20K mobile CS from the start. We'll also assume that Melhed has a single army, and Thalmarkin has two (the third army didn't participate in battles south of Sandefur). So that's one army of 20K and two of 10K, which is basically how the war began.
I would've kept my force in a single army, because Thalmarkin enjoyed a healthy advantage in nobles but parity in CS until late in the war. One should always consult the statistics for self-reflection. I know that Melhed had several opportunities to spy on Unger, Vore, etc. You folks should've known we had virtually no militia. Subtract what you know from what you don't, and you've got our true fighting strength. I do this all the time. Melhed had something like 15-20K in militia, conservatively. From this, I could figure out your mobile strength for the next campaign. How? Because even though the stats are a week behind, it takes nearly that long to prep for war and get back to the front. Everyone should be doing this. It isn't cheating, and it isn't hard.
If I were Melhed, I would've immediately occupied Bil Havil. I noticed over the course of the war that Tepmona became the rally point. Some of Thal's commanders also saw the value in that. Still, I would've chosen Bil Havil, for the following reason: for Thalmarkin, it's a hell of a long way to Lloringel. With 20K massed on the border of Lastfell, a sane general would've never ordered a sortie down south. They might've misdirected and hoped that the enemy would take the bait, sure. But then everyone's refitting, and it's roughly the same distance from Lastfell to Unger as it is from Bil Havil to Agyr. A battle of hoarded resources (gold and recruits) fought early on would've been won by Melhed. If Melhed could've shown demonstrable progress in the war, it's likely that Fronen would've joined. But as Turner pointed out, Grehk would've ginned up ANY excuse to attack Fronen. I don't have much in the way of a strategy for that. It might've opened up other rifts, but who knows? Let's stick to what we know/actually happened.
With 20K in a single army, planted in BH, Melhed would've dictated the course of events early on. It doesn't guarantee victory, but as others have pointed out, it allows one to be the actor rather than the reactor. Instead, Melhed camped in Tepmona. I'd guess this is because of the perceived opportunity to strike at Vore. Vore should've been written off immediately, for the same reasons that Thal wrote off Fronepu. It's too far, and too risky. War in BM is a series of dice rolls, and you should always try to have the odds on your side. Roll enough, and you'll win. Very few wars are won in BM by a single battle.
So, with a single army in BH, I'd have done the same thing I did in Thal: misdirect like hell. Misdirect all day, every day. At every general's disposal is a tool that confuses everyone but a spy. It's free. It's easy.
Use it. Then, when you decide to move, nobody's quite sure what you're actually doing. Generally, people discern a misdirection by looking at the stats and deciding whether the movement is stupid or not. Who cares?! We've all seen idiotic movements. Appear as though you're moving
all the time and you throw 90% of the military brain trust of BM for a loop.
I'd have misdirected to Tepmona. To Lastfell. To Rengo. Etc, etc. And then, after a few days of seeing Thal's reaction, I'd commit to a course. Knowing me, I would've attacked Lastfell right away, for reasons I've mentioned above. Then we'd refit, and come back with roughly 20K, as Melhed did for awhile. And I'd occupy BH again. If Thalmarkin separated its armies, I'd punish them by attacking Lastfell a second time. One of their armies is refitting, and the other is almost certainly called back because a 20K-to-10K battle is brutal for the loser. The victor has the upper hand. I'd raze the walls for a half day and then fall back to refit. And then I'd come back to BH, and repeat the same strategy over and over, until Lastfell had no walls and I spied an opportunity to attack it again. Then I'd loot the hell out of it, the way Thal did with Melhed's rural regions. Except looting Lastfell to rogue would've been far more devastating for us, because our town was equal to a city in terms of income.
I'd appreciate some commentary at this point before proceeding with the rest of my imaginary plan.