fate of emperor varis at the end

[Absimiliard]

As I've stated, gas weapons are not a weapon of last resort. When push comes to shove, you don't use gas weapons. Again, insane German dictator who started a World War because he was a sore loser could have gassed London at any time and deliberately choose not to because he knew what the consequences would be. Gas weapons are not weapons of last resort so if the Garleans have twisted themselves to be more insane and evil then the Nazis, then the discussion is over.

The aforementioned German dictator yet retained some semblance of reasoning in some of his actions. What I am asserting is that Garlemald could easily wind up in a position that sees its people in full panic mode, their rationality is all but completely lost. As for gas weapons not being a last resort, I haven't disagreed with you. Another key difference here is the nature of the Black Rose itself. It doesn't just kill living things - it kills aether. It renders an area totally uninhabitable rather than merely devoid of life. Its actual effects on targeted areas are probably more comparable to those of an excessively nasty nuclear device than a chemical weapon. Would anyone with even a semblance of rational thought use that as a last resort? No. Again, I haven't disagreed on that point. The crux of the matter is the ability to make rational decisions, which I simply do not believe the indoctrinated people of Garlemald could if their worst case scenario were realized.

Suffering need not require invasion or genocide. It's a universe thing and a poor justification to cause others to suffer.

I don't disagree. Again, I am not in any way justifying the actions of the Garleans. I am pointing out various things that could very easily have lead to the warped mindsets of those typically shown on screen. We do not currently know what percentage of Garlean society is actually against the atrocities they've committed, unfortunately. Incidentally, the suffering the Garleans faced in the past is not something they have ever, at least to my knowledge, attempted to use as justification for their own actions.

Boats don't sail faster in FFXIV universe and there aren't enough airships in Eorzea to either move an army or supply one, much less several armies needed to actually harm Garlemald.

Eorzea actually has quite a few airships. Certainly nothing on the order of that Garlemald has, but it would be more than enough to make a bunch of already defeated Garleans wary I'd imagine. Whether or not they are sufficient to cause actual harm is, again, secondary to perception. The Garlean government loves its propaganda machine. There's no telling what horrible things they might (or in some cases already have) convince the populace of. And on the topic of boats; If I'm not mistaken, the Limsans actually do have means of making their boats travel much faster than they would on wind alone.