I mean, China’s a potential adversary because they want to conquer Taiwan, which is an important trading partner, and Russia is a potential adversary, among other reasons, because it’s invading Ukraine, which is something the United States said it would try to prevent.
I think it’s insufficient to say that a war would cause losses for everyone, therefore everyone shouldn’t do wars. It’s been obvious for a long time that wars are bad. People thinking wars are great is not the problem. The problem is that countries have conflicting aims, and there’s no general process that can resolve those disputes in a way that is credible to and binding on all parties.
Consider Taiwan. If China renounces the use of force to conquer Taiwan, Taiwan will declare independence and be its own country and China will never have it. If Taiwan renounces the use of force to defend itself, or (likely) if the U.S. and others renounce the use of force to defend it, China will promptly invade it. So, who should win and who should lose? Personally, I think China should lose this one, but that’s not a popular position in China.
Taiwan is very unlikely to agree to be conquered by China, and China is unlikely at the present time to agree to let Taiwan become independent, so the specter of war, if not the actual thing, seems inescapable. Indeed, the supposedly anti-warmongering thing, making it clear that the US and other western powers would never intervene to defend Taiwan, will likely result in an immediate and terrible war, as China invaded Taiwan.
It’s not as simple as “if you want peace, prepare for war,” because being over prepared for war can be a self-fulfilling prophecy. There certainly are warmongers who just like to see defense spending because a lot of it ends up in their pockets. But war has been going on for thousands of years because international disagreements are inherently hard to solve, and because renouncing the ability to resort to war means that you’re likely going to lose all your international disagreements right away.