President Obama's announcement that the United States will not use nuclear weapons first in any future conflict has been praised as the end of an outdated doctrine that only applied to the Cold War.
However this isn't really the case, during the first Gulf War Saddam Hussein indisputably had chemical and biological weapons. However he didn't use them despite having done so against Iran and the Kurds. Whilst it cannot be proven definitively it seems probably that the thinly veiled threat of a nuclear counterstrike was decisive in deterring him from trying this.
That threat would not have been credible had a promise not to launch a first strike been in place.