Peace was never an option – and this is why.

1. Thargoids have no interest in communication. They do not need any of our things, so there is no possibility of trade, and the most they are willing to do is angrily demand we give their things back. Which is all well and good, but their responses to the actions of specific parties(Sirius and the Alliance, most often), has been universal attacks on human systems. Essentially, they see no difference between the actions of one human, and the actions of ALL humans.

2. Humans have no universal authority. While individual parties could ban the incursion into Thargoid territory and the harvesting of meta alloys, there is no way to stop it entirely. In fact, the technological advantage provided by Meta Alloys is such that whatever Power collects them will likely have a decisive advantage over their competitors. This will – has – created a constant pressure to impinge into Thargoid territory, and Thargoids will response as they always have; with untargeted aggression.

Now, if this were a human faction, we could communicate, explain the situation, perhaps offer reparations. If a rogue US unit attacks another country, the US will do their best to take them down, and will help to pay for the damage they've dealt.

But this isn't a human faction. We have nothing the thargoids want, and no way to communicate to explain what's happening. Yes, we supported Salvation in his genocidal attempt, but we have no indication that the Thargoids would care if he were just a terrorist that did it on his own; what matters is that a human, ANY human, attempted Xenocide, so they're going to return the favor. Not against Salvation, not against Azimuth, but against Humanity as a whole.

So if you think it through, this war was always going to happen. It was always just a matter of when.