You're taking the history of the world wars from a very Hollywood point of view where the Americans swept in and saved the incompetent Europeans. In reality America was very late to both world wars and was there for her own interests, in WWI it was merchant shipping and in WWII it was pearl harbour. While America was undoubtably a large player in the war, I don't think Europe owes you a great deal of gratitude for your conduct.
Also your aid to the world isn't fantastic actually, it's big numerically but if you look at percentages...
You're actually last in the OECD.
I can say that most Kiwis (and I think Aussies too actually) look quite fondly upon Britain despite the fact that we are now very thoroughly independent from them. Goodwill does last.
As for the Cold War, the only thing that the nuclear deterrent stopped was nuclear war. The cold war wasn't necessarily going to go to open warfare anyway, both countries had more to lose than to gain. I also disagree that chemical and biological weapons are in the same category as nuclear weapons, for two reasons. One being that none of the danger you are talking about have actually been created and the other being that no country has major stockpiles of them (so there is no mutually assured destruction).
