I know that there are more than two nations which HAVE a nuclear response. But I don't think there are more than tw or three out there who meet all of my criteria ( HAVE a nuclear response, HAVE the capability of detecting a launch in a timely manner, and HAVE some reason to question American motivations in launching an ICBM). What I'm getting at is this: The United States, Russia, France, China, India, Pakistan, N. Korea, and the U.K have nuclear weapons. We suspect that Israel has them as well. Of those nations I don't think we need to worry overmuch about ourselves, France, India, Israel or the U.K. Those nations HAVE nuclear weapons but we don't have to be terribly concerned that they're going to "retaliate" against us simply because they detect a launch. Pakistan and N. Korea probably don't have the capability of detecting a launch in a timely (actionable) timeframe. That leaves Chian and Russia as prospective threats given the discussion we're having here. And I think that even with those two MAD and a few phone calls kinda obviates any prospective threat. I can't see China retaliating for a strike on N. Korea. Absolutely not against a conventional strike. Almost certainly not against a nuclear strike. Not while the missiles are still in the air and probably not even after they hit. In fact, I can't think of any nuclear power that would respond against America for any reason other than a confirmed nuclear first strike on their homeland. Is it possible that they would? Sure. But is also possible, and in my opinion infinately more likely, that the Earth would be impacted by a catistrophic meteor strike between the time the U.S. launched an ICBM and any other nation not its target retaliated in any way. Of course there's no correlation betwween the two but this only serves to reinforce how improbable I think it is that China or Russia would retaliate on the U.S. for a simple missile launch.