First nuclear weapon detonate: which country is responsible for it
Nuclear tests don't count, only actual weapon used for war or strategic purpose connecting to war.
People are also trading
The US uses a nuke every 40 years in the average, the leftover period is 8 years, so rough estimate of the base rate for them using a nuke at all is 20% (though here the question is different). They also have a bigger arsenal than most others and are less likely to suffer serious consequences if they just use one or a few nukes in isolation for tactical reasons. Small actors like North Korea or the UK on the other hand have much more to lose by triggering a nuclear confrontation. Edit: base rate is likely off because of strong time autocorrelation in nuke usage
@Quadrifold It's kind of hateful to design a market to likely resolve N/A when you could easily just add a "nobody" option.