"For example would you please tell us under which treaty or treaties the United States is obligated to, using your words, "Blow up the World?""

Any treaty with allies that consider an attack upon them to be the equivalent of an attack on the US. NATO, SEATO, etc. Since OUR response to a WMD attack, as given by MAD, is to initiate ( or rather respond ) a devastating WMD attack upon whomever we perceive to be the attacker.

Once we use WMD upon, say , Iran, I would suspect we would be attacked by other nations, and thus the entire world would be involved.