Okay, I liked the film well enough but… no, the plot didn’t really make sense. It makes sense in that the main characters have a good reason for what they’re doing at any given point, but if you look at what goes on overall, it’s a mess. I mean, Ares supposedly wants the armistice to happen because reasons. I’ll assume he knew that WWII would happen later on. At the same time, however, he’s pushing the Germans into developing a new supergas that they can use to commit war crimes that will insure the armistice doesn’t come to pass. It’s not even like he stops trying to inspire Dr. Poison once the armistice planning starts. He goes right on and keeps doing it.
Of course the whole gas plot doesn’t really work either, because the whole point of the gas is that it eats through gasmasks. But they don’t plan to use it on the front. They plan to drop it on London, where people don’t tend to walk around with gasmasks, so they really could have done that whenever they wanted anyway.
And then by the end of the film, they foil the gas bombing and ensure the armistice is signed… which was apparently what Ares wanted all along… so the whole film could be avoided if Ares wasn’t inexplicably working against his own goals.