[quote=So Boerd]
I see your point. What about if/when China gets conventional superiority?
[/quote]

Definitely changes the picture. That said, Great Britain has managed not to nuke the USA ever since we became the world's hyperpower, so I'd like to think we can manage a similar record against China. If you get deep enough into speculation-politics, there's actually a really good chance that China never takes over -- the geopolitics are not [i]remotely[/i] in their favor (China essentially is a large body of Tibets, and you know how well that's been working out lately). By 2050 there may not be a PRC -- okay, you can say that about anyone; point is, don't lose sleep over the thought of nuclear war with a hostile China. I know that a war-scenario with them makes for great TV, but it's much more realistic to expect that we will *never* have an armed conflict against China -- if they stick around as a power, it's either going to be because their capital investments in Africa paid off big (which we don't really care about, we have little involvement), or because we're directly supporting them as a government. 

Still. Hypotheticals are fun. Let's say China gets parity with the US, and they're beating us in a hot conventional war. How close do they have to get before we can nuke them?

It's a pretty easy answer for me -- I would *certainly* nuke a Chinese warfleet that crossed Midway. No risk of civilian casualties, minimal damage from fallout (we'll kill some dolphins, I guess), and strategic significance make that the most palatable nuclear scenario ever conceived. If we can't nuke that, we can't nuke anything. Of course they'd presumably take the same attitude towards *our* warfleets, which would render most conventional wars pretty futile. 

Alright. Let's make it more interesting. Suppose China is going to war with Japan, [i]and[/i] assume that we [i]must[/i] intervene. How much would China have to do to Japan, before we're allowed to nuke the PRC on Japan's behalf?

[b]A fucking lot.[/b] I have no qualms with fighting wars to protect America's interests abroad -- but fighting a *nuclear* war to protect our 'interests' is preeeeeeettty sketchy. It comes down to basically a Hiroshima scenario -- can you drop a Nuke in order to end a war? I'm not sure that works more than once. Shit, I'm amazed that it worked the first time. [i]If China has committed to a total-war scenario and conventional arms have been exhausted, I guess I'm okay with nukes for emphasis.[/i] Not lightly. It's a big fucking decision to make, and obviously I want nothing to do with making it. But I'd stand behind it, if I had to, if the nuclear strike was successful in forcing a surrender.