If diplomacy had been effective 100 years ago, the tragedy of the Great War and the consequent Second World War could have been averted. And, arguably, it was diplomacy from an unexpected source that helped pull the world back from the brink of the Cuban Crisis.
Recently on this website, I reported good news emanating from the UN or from the major powers. These were :
(a) The UN resolution committing the Security Council to address the illicit transfer of small arms and weapons
(b) The Syrian agreement to give up chemical weapons
(c) The thawing of relations between the US and Iran