The theory is that the US has committed to ruining things for everyone if bad things happen to them. Otherwise, hostile countries would have an incentive to create false flag attacks, or to incite an enemy to attack in truth. But if Iran knows that North Korea nuking DC means that they get nuked too (along with essentially everyone else on the planet), there's less incentive to make it happen.
Same goes for Russia/China - wouldn't either of them 'love' a world where the US got in a nuclear exchange with the other? No more competition!
How do we know the weapons originated from North Korea, and not Japan, or the UK, or some other unlikely source?
Because we saw the missile radar tracks? What if it was a shipping container or UUV bomb?
This is why huge sums of money have been spent on post-detonation nuclear fingerprinting with high accuracy.
Absent a high likelihood of correctly attributing the source, one must default to retaliating against everyone.
Only once one establishes a credible belief in an adversary that the true source will likely be discovered can one relax policy to retaliation only against the source (and probably its allies).
You're saying that assuming a nuke goes off and nobody knows where it came from, that logic dictates the US or anyone else will nuke the whole world. I utterly don't believe that this is a thing that is planned or arranged to happen.
No, I wasn't making a moral argument. I was talking about facts as I see them - I don't believe that the US or anyone else will blow up the world in response to being nuked. That is based on my thinking the game theory logic doesn't hold together and never has, but also historical events that indicate it was definitely invalid as of sometime in the 1960s.
The theory is that the US has committed to blowing up...Japan, say...if North Korea should succeed in missiling San Francisco?