China started a war with Vietnam almost immediately after USA surrendered. (Not contradicting you; if anything supporting the point...)

As a sort of redux, I guess my feeling is that obviously, every state would prefer to be surrounded by allies, or better still, by seas.

However, the idea that all superpowers inevitably go to war to preserve this state is just wrong. If you consider superpowers starting from antiquity to today, the only state that has achieved this situation (at any point?) is the USA. Every other has had at least one significant land border with an adversary.

(PS: Probably the biggest one is, of course, between the USSR and China, which was a very hot border since the sino-soviet split).

In general, I think you are correct. Neighboring states will learn to coexist or at least one of them will cease to exist as a state. Some Americans imagine that "exceptionalism" exempts us from this dynamic, but most of us are wiser.

PS: it was nice while it lasted... https://www.newyorker.com/news/daily-comment/russia-and-chin...