Has it? The last 60 years have been relatively peaceful, by historical standards.
That's actually a false hypothesis of people in the 'western bubble' who haven't experienced war. Research I've seen shows that people in places that have experienced it, such as in Syria, are much more opposed to it.
And that bears out in Western experiences: Who created the UN, with the stated purpose to prevent another war? Who created (the ancestor institutions that became) the EU to prevent another European war? Who enforced the Geneva conventions and prosecuted war criminals after WWII?
The answer is, the people who had lived WWI and WWII. They knew far more of war than anyone today in the West, and they thought it was the worst scourge of humanity which must be prevented from happening again at almost any cost. Who are we to disagree?
Example: there's far fewer cold war deaths than from traffic accidents, let alone real wars.
WW2 killed 3% of all humanity: https://en.wikipedia.org/wiki/World_War_II_casualties
The end of the Han dynasty killed a large percentage of all chinese people.
For perspective: https://en.wikipedia.org/wiki/List_of_wars_by_death_toll
http://asirt.org/initiatives/informing-road-users/road-safet...
In brief, it concludes that the US alone (there have been lots of conflicts without any manifest involvement of the US) has been involved since WWII in conflicts causing "the deaths of between 20 and 30 million people".
[Edit] You may also consider the ongoing war in Syria, which is not only exceeding WII in duration already, but also overshadows the total death count of the US in the WWII Pacific "theatre" (161,000 dead, including 111,914 in battle and 49,000 non-battle) by 500,000+ dead (last consensual figure was 470,000, issued by the Syrian Center for Policy Research in 2016).
As best we can tell, nukes actually did end large-scale war. I would call that at least a partially mitigated disaster.
I know it came very close, but the assumption was that it would come to the brink yet nobody would want to go through with it and begin open aggression. Seems dubious and risky, but once again it worked. And let's not discount the negative risk--a conventional world war with the Soviet Union, China, the US and Britain would have been so terrible.
With such a small data set we should still be dubious, but I don't know if we can consign it merely to luck. I think it was a good plan. Terrible publicity, though. Nightmarish. But so is war.
It makes more sense if you remember that nuclear weapons and delivery technology didn't reach the 'assured destruction' stage for awhile. Remember that in the Korean War, in the 1950s, General MacArthur was pushing to use nuclear weapons (IIRC); it wasn't as taboo then. Finally, remember that MAD applied only to the Soviet Union and U.S. (or the Warsaw Pact and NATO), while major international wars ended worldwide, for the most part. Remember that WWI and WWII were fought between future NATO members; the later peace between them wasn't due to MAD.
> At the beginning of the twentieth century it was looking like we'd have another world war every twenty years or so for the rest of time.
The victors of WWII were very concerned about that, and began planning to prevent it before the war ended. That resulted in the UN, the institutions that became the EU, a rejection of nationalism (as a significant cause of war), the spread of democracy and universal human rights as a peace-making policy (democracies generally don't start wars with each other), and U.S. leadership in the international order to maintain those things and to provide stability. My understanding is that those are the reasons for the relative but extraordinary peace. Here's a Churchill speech about it in Zurich in 1946 (the speech focuses on the future EU; remember he also was one of the architects of the United Nations):
http://www.churchill-society-london.org.uk/astonish.html
(I'll also note that they seemed to have worked so well that now people take the peace for granted and are tossing aside the things that make it happen.)
[0] The best credible source I can find quickly. If you hit a paywall, access it via a search engine: https://www.britannica.com/topic/nuclear-strategy#ref1224926
EDIT: Added a detail
Again, I broadly agree with you and would definitely prefer to see a continuation of the past 60 years over whatever’s on the horizon, but let’s not get too rose tinted about Weatern benevolence.
Mutually Assured Destruction is not the same as Brodie's Nuclear Deterrence AFAIK (which admittedly isn't much). In 1946, neither side could come close to assuring destruction of the other; the Soviets didn't have any atomic bombs until 1949, the U.S. didn't have the H-bomb until 1954, and of course neither had ICBMs, The best production rocket was probably the V-2.
MAD is less a strategy than a reality. As long as each side has weapons that can't be credibly destroyed in a first strike, you have MAD, whether theorists explicitly call for it or not.
Though of course submarines make this easier to achieve in practice.
I might be wrong about this though, perhaps there were significant differences between Brodie's 1946 theory and later MAD developments.
> As long as each side has weapons that can't be credibly destroyed in a first strike, you have MAD
With the significant qualifier that you need enough weapons to survive to completely destroy the enemy.
> MAD is less a strategy than a reality
I'm pretty sure that's incorrect. It was and is a specific strategy and implementing it was the reason for the ABM treaty and others - defensive weapons would make destruction less "assured". See the source I linked above.
People do of course adopt it as a strategy as well. But if effective defense tech existed I don't think the strategy would hold. The US abandoned the ABM treaty even without such technology.
As for your first point, it's true that MAD didn't really conclusively come into force until submarines. But there were efforts before then to maintain a second strike capability, such as keeping a certain percentage of bombers in the air, preparing them for fast takeoff, etc
Maybe not 100% assured second strike, but the basic idea was the same
Nuclear weapons create a requirement that you safety depends on the pragmatism and sanity of leaders and government. Not only of your own country but your enemies.
In the days of WWII, an attacker could rightly feel confident that there could not be an immediate response that strikes anything of importance. The attacker might even believe that such a response could not be possible ever in the future. Poland could be invaded without any realistic worry that Berlin would be attacked that same day, and a bit of optimism turns that into Berlin being safe.
https://www.journals.uchicago.edu/doi/abs/10.1086/230699