Via Justin Logan, Kenneth Waltz talks about international politics with Theory Talks, and he made this sensible observation about proliferation worries:

The fact is that people worry that a new nuclear country, once it gets a nuclear shield, would then begin to behave immoderately or irresponsibly under the cover of its own nuclear weapons. Well, that has never happened. Every country that has had nuclear weapons has behaved moderately. If you think of the Soviet Union and China, both behaved much more radically before they had nuclear weapons. Stalin’s bravado in the face of American nuclear weapons was extremely impressive, or depressing—depending on how you want to look at it—but once they got the nuclear weapons, the Soviets calmed down. And the same thing was true for China.

So, what people fear is the opposite of what, in fact, has happened. That is rather typical in the nuclear business: we do not look at the past and say “Well gee, every nuclear country has behaved like every other nuclear country. What do we worry about?” In fact, the effect of nuclear weapons is that it moderates the behavior of their possessors; and that is very easy to understand!