For a while we lived in a unipolar world. The US ruled the roost, for better and for worse. The world was relatively calm.
But now we're transitioning to a multipolar world. Things will become more and more unstable. More wars and the risk of escalation is part and parcel of that transition. So it's back to preparing for the possibility of nuclear war.
It's a shame really. Perhaps we could have tackled climate change if the world was more unified. Perhaps not, given the lack of progress so far. Or perhaps a different world order will help and offer new opportunities, if we survive the transition.