They were laying siege to Val Royaux itself when the call went out.
I suppose. BioWare has a habit of rewriting wars like this to make very little sense.
Like how in
Mass Effect 3, Primarch Adrien Victus claimed that krogan had launched attacks on Palaven itself - the capital of the Turian Hierarchy - and that only the deployment of the genophage stopped them. Never mind that the genophage was a slow-acting mechanism that would only tell on krogan numbers after more than a generation, and that it did not kill any fighting forces already in the field. It was not a tactical weapon. It is pretty much impossible for the deployment of the genophage to have halted the invasion of Palaven.
Other in-universe sources indicate that turian and Council forces had achieved overall military superiority by the time the genophage was deployed and that even if the krogan had tried to threaten an invasion of Palaven it would have been little better than a raid, akin to the summer 1864 Confederate attack on Washington (to continue with the American Civil War analogies used by dragonflight above). But, obviously, that isn't what Victus says. He specifically calls the battle for Palaven against the krogan a "last stand". Militarily, that's ridiculous.
Instead, Victus says those lines not because they are a plausible way to formulate the narrative of the war, but because the
Mass Effect writing team wanted to reemphasize the potential threat of the resurgent krogan by making them as much of a threat to turian society in 700 CE as the Reapers were in 2186 CE. The game featured a great many sympathetic situations for krogan, and Victus' comment was one way to try to balance that out - whether it made historical sense or not.
There's a similar problem with the Exalted March narrative. It strains plausibility to claim this train of events:
1. Dalish elves and Orlais go to war following Red Crossing crisis
2. Dalish elven armies sweep all before them, pushing through the Heartlands
3. Dalish elven armies besiege Val Royeaux
4. Orlesian Chantry issues calls for an Exalted March
5. Orlesian Chantry organizes Exalted March armies
6. Dalish armies capture Val Royeaux, Exalted March armies pursue and turn back invasion
7. Exalted March armies comprehensively annihilate Dalish elven resistance and occupy Halamshiral
8. Exalted March armies win final campaign against Dalish elves in Dirthavaren and begin Orlesian program of annexation, eviction, and settlement
First, the Dalish armies curbstomped the Orlesians so badly that they managed to pose a serious threat to the capital. Then, they besieged the capital, and continued to besiege it while the Orlesians amassed a relief army of crusaders. But where did these crusaders come from? Historically, crusading armies on Earth were primarily composed of people who already had military experience and a career. Kings and princes took their soldiers, their nobles, and their nobles' retainers with them to the Holy Land or Egypt or the Baltic or wherever. So apparently, a vast chunk of the Orlesian army was nowhere to be seen during the Dalish elves' initial march of victory, and only decided to fight once Val Royeaux itself was under threat. I suppose that's not impossible, but it seems a little silly that the vast Orlesian military establishment took that long to actually respond to the crisis.
This problem can be mitigated by including new recruits and volunteers among the Exalted Marchers, making the war an Orlesian war of national resistance rather than a nobles' crusade. But that has its own problems. Untrained levy armies are well and good, and having them break the siege of Val Royeaux could be plausible enough if that had happened. But these Exalted Marchers went on to destroy the Dalish armies and occupy the Dales: they fought long campaigns away from their homes and farms. Extended campaigning for the ten years credited by the Codex (Siege of Val Royeaux 2:10 Glory - Fall of Halamshiral 2:20 Glory) would be difficult enough for professional soldiers; levies would lose discipline almost immediately, to say nothing of going home for the harvest. Adding these recruits to the narrative would not alleviate the plausibility issues. It is simply not creditable for them to have wiped out the invading army and gone on to completely conquer the Dales.
Now, there are plenty of examples of countries that start out wars slowly but gain steam as time goes on. But it's hard to get that to work with Orlais. As something akin to a medieval European state, the majority of its usable military manpower - the manpower with experience and training - would already be ready to participate in the first few campaigns. It would take years of fighting experience to make an effective soldier, and training systems would be far more rudimentary than nowadays. And doing all this on the strategic and operational defensive is even harder to credit.
The closest analogy in medieval warfare I can think of is the war between the Byzantine Empire and Sasanian Iran from 602 to 628 CE, when civil war shattered the Byzantine armies so badly in the first half of the war that Iranian armies penetrated the frontier fortress belt and eventually besieged the capital, Constantinople. The Emperor Herakleios eventually managed to stabilize the military situation, slowly rebuilt armies from the fragments of those that had existed before, and mounted one of the most brilliant efforts in the history of warfare to bring the war back into Iranian territory and eventually defeat the Sasanian Empire. But that war devastated the victors; the Byzantines could barely force Iran into making peace on the basis of the
status quo ante bellum, and a few years later the exhausted empire didn't have anything left to ward off the Muslim invasions. On this analogy, it would be like the Byzantines losing the whole war to Iran, including the capital, then miraculously making a comeback,
and then conquering all of Iran into the bargain. And remaining the preeminent power in the world for centuries to come. That's...kind of on the ridiculous side.
So, like the krogan thing, I think that the narrative of the Exalted March of the Dales was crafted primarily for story purposes instead of plausibility ones. Only in the last few years, with the release of
World of Thedas Volume 1 and
Inquisition, has BioWare's portrayal of the Exalted Marches included emphasis on Dalish offensive actions at Montsimmard and Val Royeaux. Before that, it looked far more one-sided, and the Dalish looked far more like victims. Now...not so much.