The reason I included the Landsmeet as a civilian court; not a military one.
It's worth pointing out that this is not a particularly clear distinction. Even though much of their legal authority stems from their rights of administration and petition over their lands, the banns and arls are
also the commanders, staffers, and suppliers of the king's army. In other threads, I've analogized Ferelden's Landsmeet not to the English Parliament (which I think is hopelessly anachronistic) but to the "army assembly"-style
comitati of the early medieval Western European kingdoms - Merovingian Francia, Gothic Italy and Spain, Vandal Africa. Given the participants in the Landsmeet, as well as its remit, I think this is a better comparison.
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On a similar note, I think that attempting to figure out whether Loghain's actions specifically qualified as "treason" or "desertion" is a dead end. We don't know Ferelden's laws. Real-world comparisons are slim pickings. For example, Ine's Law is silent on the subject of treason (it merely imposes fines for failing to participate in military service). England only got its first clear, consistent definition of "treason" in 1351. In that law, a man is guilty of treason if he "compasse[s] or imagine[s] the death of the king", but whether Loghain's actions qualify as that is open to debate.
And as I've tried to point out in my own thread, it was and is impossible for Loghain to have known how successful attacking the darkspawn would have been. He did not have a view of the battlefield - that was the whole point of using the tower. Even if he did, it would be effectively impossible for him to have known if his attack would succeed. This was not 'just the facts' or a straightforward calculation. It would be the gut instinct of a reasonably experienced soldier who all the same had had no formal scientific schooling in warfare and who possessed intrinsically limited amounts of information about his opponent. Premodern battle was a lottery that defied prediction; premodern generals trusted in 'instincts', not ratiocination.
And
then there's the whole separate issue of where, exactly, Loghain proposed to beat the darkspawn if not at Ostagar. And how he planned to do it without the king, his men, or the Wardens. Construing the Battle of Ostagar as a choice between losing the army and keeping it alive is an entirely false dichotomy, and an overly simplistic one that stacks the deck in favor of Loghain's decision.