A lot of your examples are outcomes where war could have been avoided much earlier in the process by the process Scott talks about.
The invasion of Ukraine was partly influenced by US/NATO escalation in the region. It doesn't justify what Putin did, but the US did do things that were designed to escalate tensions rather than deescalate. Because it benefits the US that Putin invade, the whole world put sanctions on Russia, and the Ukraine becomes permanently beholden to the US and the West for support. I think there definitely were things that could have been done to reduce the likelihood that Putin would have gained the Russian public's tacit support for the invasion of Ukraine.
Likewise Hitler only rose to power because the Allies in the Treaty of Versailles, destroyed the German economy in retribution for WWI. Was it justified to punish Germany for WWI? Sure. But those actions escalated things, and set up the conditions that allowed a person like Hitler to actually gain mass following. If the German economy had been healthy, the rhetoric about the Jews wouldn't have taken root.
There is a point in conflict where the opportunities for deescalation and negotiation break down and war is inevitable. I don't think Scott is claiming we should never fight.
But he's talking about what's required to actually end war on earth for good. It requires proactive behaviour. The conditions for any given war are set up decades before the war begins. You can change those conditions.
A great example of this, is when the US poured money into helping rebuild Japan after WWII. Even though Japan would have "deserved" the same kind of punitive measures as inflicted on Germany after WWI, the West learned from what happened, and decided to do the opposite with Japan. They rebuilt infrastructure, and helped foster business connections between Japan and the US. As a result Japan is now a peaceful country and a strong ally to the West. (Yes the nukes and their military restrictions also were important factors, but this was able to be achieved without resistance or rebellion because the US helped rebuild Japan's economy).
