So if you're trying to build a Tom Clancy style political situation in a story about a nuclear exchange between a country and a superpower, would this be possible, or would it trigger the second superpower to launch as well?
USA vs North Korea
Russia vs Mexico
Alliances are considered irrelevant in this question.
If America launched nukes at North Korea, would China be able to estimate their trajectories and speeds accurately enough to not feel obligated to fire back? Since the American missiles could actually be aimed at China instead for a surprise attack.
Same type of scenario as the first but the USA would be reacting to a Russian launch instead.