It’s been about 70 years since the end of WWII and the introduction of nuclear weapons. With 70 years of history to review has the proliferation of nuclear weapons helped to prevent large scale “global” wars or not in that the costs of two nuclear powers engaging full on are too high?
Many of us believe that, yes, Mutually Assured Destruction, along with the hellish examples of Hiroshima and Nagasaki, have forced the world’s major military powers to deal with problems without massive mobilization of troops and weapons.
Without nuclear weapons, the Soviet Union would very likely have rolled over West Germany, with its titanic advantage in tanks, until stopped by NATO, with its advantage in aircraft. There would likely have been a major Naval war associated with this. A very different time-line than our own…
Indeed, the weapons of our ultimate destruction are the only thing stopping us from our ultimate destruction.
Stopped global wars. Stopped major regional wars.Stopped great powers from stomping on regional ones, which was traditionally one of the most popular ways of acting.
On the flip side, it has increased the tendency of nations to support non state and independent actors in their operations. That is not a good thing.
Well, one item I take into consideration on why I do not quite agree is that with a few more mistakes happening in many of the past crises the situations could had gone nuclear, and we could not be having this conversation.
As the guys at Kurzgesagt ("In a Nutshell) explained in their video of why there is more peace now, it is not just as simple as nuclear weapons being present.
Putting my game theory hat on, I don’t see why nukes would prevent conventional wars.
Country A wants to seize an island owned by Country B. A may be nervous about B using a nuclear weapon, but if both have nukes then MAD comes into play. It doesn’t make sense for B to go nuclear to prevent some small part of its state being annexed. It only makes sense at the point where the destruction being wrought by A approaches that of a nuclear war within B’s territory.
OTOH from a psychology and risk analysis POV; if the guy at the next table looks big and strong, you don’t mess with him, regardless of what his most likely behaviour would be.
The problem is that B will know that if it lets A start annexing little bits and pieces of itself, A can keep on doing it until B is all gone. And A can’t rely on B to not decide that it’s doomed once A starts something like that, and to try to take A with it.
Well “A” will do a cost benefit analysis. The potential gain (an island) is far outweighed by the possible losses due to nuclear conflict. Even if there are no attacks on metropolitan parts of “A” a nuclear conflict restricted to theater means casualties far in excess of what is acceptable.
Country A could very convincingly (and perhaps genuinely) argue that it only wants one small portion of territory, though.
If China invaded and conquered Guam, for instance, a subsequent Chinese takeover of the rest of the United States would still be extremely implausible.
The only reason America and Russia aren’t apocalyptic wastelands is down to luck and in some cases the restraint of only a couple individuals.
Another reason for the lack of war between major powers is because there’s not much gain to be had. There’s too much economic integration, it’d be like an economic version of MAD. And the other advanced countries can actually punch back. Better to go after small fries outside the major economic zones, or to keep out the brush fires. Which is what actually happens.
The only rationale I can think up where powerful countries would go to war against others would be crazy stuff, like fanatical religious/racial/nationalist ideologies.
They can’t rely on B believing them however.
The OP’s example worked as long as the memories of Hiroshima and Nagasaki (as Trinopus mentioned) were fresh. Russia’s annexation of the Crimea suggests either that they no longer believe that we will nuke them, or that the memory has faded and they’re willing to risk a city or two (knowing the first nuker will look worse), or both.
I think that’s something of a special case. At the dawn of the nuclear age, Crimea actually was part of Russia, they had at least a plausible reason (the plebiscite) for re-annexing it, and Ukraine was not a NATO country. If Russia invaded Estonia or something (which is not happening, but if it did) then that would really indicate they no longer feared the nuclear deterrent.
With all the close calls there have been we are lucky we are not toast. MAD is one thing, but we are humans and we make mistakes. The nukes may have prevented a war, but at the same time as we were learning about them we set off so many of them that everyone on the planet was experiencing fallout. So we almost killed off the human race by experimenting with them, and without a war at all.
They’ve worked well so far. 
One hesitates to be overly optimistic they will work well forever.
But hey, maybe we’ll end up toasting from AGW instead of nukes. We never quite seem to get the end game right when we try to predict.
Do you have a cite for this?
I had no idea nuclear weapon development all by itself nearly bumped me off from fallout or anything else.
Fallout from nuclear testing is, of course, a non-trivial concern, but it never came anywhere close to “killing off the human race.”
Now, the concept of MIRV weapons – one missile launching many warheads – could have threatened the human race, as it strongly rewards a first strike. This was realized in the 1980’s – the Scowcroft Commission addressed it in 1983. So, yes, strategic errors were made, of a very dangerous kind.
(Currently, a testing moratorium helps increase the uncertainty of weapons reliability, making a launch slightly less likely. No one wants to fling a handful of duds at the enemy. In this limited sense, testing is strategically dangerous.)
It was not THAT extreme. Nowhere near that severe.
In The Better Angels of Our Nature, Steven Pinker argues that nukes haven’t actually prevented much warfare. I no longer have a copy handy, but if memory serves, he contends that major nations are already less belligerent and are economically integrated enough that war between them would be unlikely even without nukes.
I’d love it if it were true, but I don’t believe it for a nanosecond. Without nuclear deterrence, Stalin would have run his tanks right over West Germany, and not stopped till well into France.
I also think the Korean War would have been much worse, probably with a total Chinese victory over the peninsula and expansion into Japan.