First, I don't think this leads to WW3 although I would agree with you that there is a general global tendency towards escalation. Still, I think we can not call this WW3 and I am not 100% certain this is a build-up to WW3 either.

As for North Korea: I think the situation is not solely about North Korea itself but China. China is kind of acting as protective proxy here. I don't see North Korea as primary problem to the USA, but to South Korea and Japan. Both really should get nukes. Taiwan too, though mainland China would probably invade when it thinks Taiwan is about to have nukes; then again China already committed to invasion - this is the whole point of having a dictator like Xi in charge now.

The situation Russia is in is interesting, because even though they are stronger than Ukraine, Ukraine managed to stop or delay Russia, which is a huge feat, even with support. As Putin does not want to stop, and Trump is supporting him (agent Krasnov theory applies), I think this has escalation potential. Putin is killing civilians in Ukraine daily - I think he does that because he already committed to further escalation against all Europeans. So Europeans need a nuclear arsenal, but european politicians are totally lame - see Merz "we will never have nukes". Basically he wants to be abused by Putin here.