Pyongyang will almost certainly never be nuked by the US, even if the DPRK used nukes first. The reasons are manifold, and include the political costs (domestic + international) of using nuclear weapons against a captive and largely innocent people, as well as the actual nuclear fallout that would effect nearby neighbours.
Tom Nichols delves deeper into the topic in both article [0] and book [1] forms.
> Pyongyang will almost certainly never be nuked by the US, even if the DPRK used nukes first. The reasons are manifold, and include the political costs (domestic + international) of using nuclear weapons against a captive and largely innocent people, as well as the actual nuclear fallout that would effect nearby neighbours.
On second thought, if the DPRK were to nuke New York or something, I can't see how the US could afford not to nuke back without looking weak. At the same time, that would probably trigger a nuclear apocalypse scenario pretty quickly with retaliation from China and the like.
A strong response would definitely be necessary, but that response is unlikely to be nuclear in kind. The USA and its allies have enough conventional firepower to permanently end the DPRK regime without needing to resort to nukes. Nichols spells it out in more detail.
One would hope that in this case, the US had enough restraint and humanity to not nuke a city in retaliation but launch a decapitation strike against the leadership and the military - perhaps nuking a couple of the larger bases and military ports.
Tom Nichols delves deeper into the topic in both article [0] and book [1] forms.
[0] http://nationalinterest.org/feature/if-america-could-rebuild...
[1] http://www.upenn.edu/pennpress/book/15090.html