I disagree unless we mean, in a very narrow sense, "peer" challenges. Clearly the US hegemonic status went largely unchallenged for a while, but I don't agree with your characterization of the period as more peaceful than previous times, and therefore warranting a radical break with the past to preserve.

I honestly want to explore this topic further. I am not so closed off to the possibility that I'm wrong that I am unreceptive to counter arguments, so I hope you'll engage the topic with me a bit more:

peaceful is an vague term, but some of the language I have used is not much more precise. However I did mention one somewhat narrow metric, per-capita wartime deaths, and the world has been much better in this area during the the last 20-30 years than previously. What are your thoughts on that aspect of this discussion?

On the more ambiguous connotations of what I wrote, I will clarify the idea that was uppermost in my mind when I made my comments:

Essentially, a conflict that is catastrophic for the entire world is less likely (at least prior to recent events) during the last 20-30 years. The fall of the Soviet empire left no two adversaries so antagonistic to each other, each with world-destroying capabilities, that we have had to constantly worry about such a conflict breaking out. We have not had to walk so carefully on egg shells to avoid reaching that point. North Korea has only recently become the nation most likely to initiate a nuclear conflict, and I would still rate that as a lower probability than cold-war era direct US <-> Soviet conflict, and the capabilities of North Korea in this area are still too primitive for a conflict with them to inflict the same scale of damage as direct Soviet/US aggression.

Certainly horrific local and regional conflicts have still prevailed in some areas of the world, perhaps only slightly reduced (arguably not reduced at all, and worse in some regions) but their potential to spill over into a wider world-scale conflict remained exceedingly low compared to prior decades. They are less dangerous to the wider world because some of those cold-war era conflicts were proxy wars that risked escalation to direct conflict between military super powers.

Consider that the Vietnam War could easily have been won by either the US or Soviets if either of those powers had been willing to bring their full and complete military might to bear against their proxy opposition within that country. Indeed there was a constant tension that such a thing might happen and bring the puppet masters behind the North & South Vietnamese into direct conflict with each other.

This was perhaps even more true during the Korean War, with the added risk of more significant Chinese involvement & explicit threats by the US that nuclear options were on the table. The only thing that mitigated the potential for global nuclear war was that US nuclear capabilities were still relatively limited, Soviet nuclear capabilities even further behind, and Chinese nukes a decade or more away from completion. (by which point we'd progressed past the sino-soviet split so an alliance between those two powers was pretty much off the table) But during that conflict there was still significant possibility that a conflict on the scale of WWII, with slightly more advanced technology, could erupt & include a major nuclear component as well.

And of course there was the idiotic brinkmanship if the Cuban Missile Crisis.

Nothing of that scale has been anywhere near as probable after the end of the cold war. Having grown up in the twilight years itf the cold war, I can directly attest to the global tension of those times, and the global sigh of relief as they ended. In the years since then we have never approached that level of tension until today, with the Ukrainian invasion, where small echoes of those times can now be felt.

This is the thrust behind my comments. That perhaps local & regional conflicts have seen little change, but world-wide existential threats from military conflict are-- comparatively-- a much reduced concern.