This is a big debate among nuclear historians and especially international relations researchers — are nuclear weapons stabilizing or destabilizing? What we know is:

• direct, "hot," great power wars essentially ended after World War II

• indirect, "cold" proxy wars and revolutions skyrocketed after World War II

• while only a few states developed nuclear weapons in this period, many states aligned themselves with nuclear-armed states

So how to interpret that? The nuclear optimists basically say, "as we can see, nukes prevented great power wars, even if they increased the value of smaller-scale conflict." The nuclear pessimists say, "nukes increased tensions and from that increased not only proxy wars, but also increased the consequences should something have gone wrong, and it is only luck that kept things from getting more 'hot.'" And finally there are a small few who say, essentially, nukes are overrated in this equation, and in fact are not the important, driving variable that they appear to be: even without nukes, many of these trends would have occurred for other reasons (such as decolonialization).

Like any boring historian I am somewhat on the fence of all of this. I can see all of the different arguments. It is not so easy to see how to tell which interpretation is most correct. And it is not clear to me that all of these could not be to some degree, at different places and times, true.

A good place to start thinking about these positions is Sagan and Waltz, The Spread of Nuclear Weapons: A Debate Renewed. Waltz is famous for his "more is better" argument about nukes (nukes = stability); Sagan is highly skeptical. Both are very intelligent and intellectually-honest scholars, and the book is them writing and responding and writing and responding to one another, so it's a real debate and not just political posturing.