> The question presupposes that avoiding war would avoid "brutal violence, intense prolonged suffering, anguish and grief" later. In many cases, that's not the case. Instead, the decline can bring with it violence, intense prolonged suffering, anguish and grief -- only without anybody doing anything before to resist those things.
Sure; if you can convince me that any given war will avert more harm than it causes, I'll (intellectually at least) agree that it's justified. But at large temporal and geographical scales, with insanely complicated and only vaguely understood systems at work, you need an extremely strong argument to justify an action that will definitely lead to terrible consequences in the near term.
The comment we're discussing falls far short of such an argument. In fact it doesn't even seem to aim at making one -- and not just in the sense that it's (understandably) very abstract and lacking any kind of detail. As far as I can tell it is motivated by nationalism, and certainly not by any desire to prevent greater suffering. Its idea of failure sounds more like a (relatively) peaceful transition:
> You know I lately think that, ok, we're mostly past the age of empires physically conquering one another, we're in the age of economic ebbs and flows of established countries.
> And in this kind of age, the thing that sinks a country is not aggression by others, but indifference and lethargy as a country "gets old".