Basically. Plus all the alliances defending one another.
At the end of the day nobody wants to instigate anything. If you're a country and you have a nuclear ally, you're as good as protected.
That's why we'll let North Korea do all their rocket experiments, test out crazy long range weapons (that now can hit any point in our country), etc.
North Korea knows though they throw a real one, it'll be over for them soon after that.
However, we know we'll start exchanging nukes with China right after and we don't want that either.
So we let them do their crazy flight tests and perfect their tech because we know they won't use it.