"By three methods we may learn wisdom:
First, by reflection, which is noblest;
Second, by imitation, which is easiest;
and third by experience, which is the bitterest."
I've tagged this with "Military Theory" for a reason.
The historic example of the early smokeless powder era (~1890 to 1914) haunts me. It's eerily similar to the present time in many regards. There wasn't enough practical application of military theory to enable learning by imitation (rarity of major wars was a very nice feature of the period, of course). There was a huge collective effort to understand modern warfare by reflection, but the few who got it right weren't in power. Thus the face of modern warfare was learnt about the hard way.
This was a major failure, which we should not repeat in this eerily similar situation.
(1) no wars between great powers for decades
(2) lots of small wars, albeit with little use for understanding inter-great power wars
(3) lots of demographic changes
(4) lots of economic changes
(5) lots of technological changes
(6) steady erosion of respect for war, if such a thing was established in the first place at all
Nukes won't prevent wars between great powers forever; our respect for nukes is about the same as the respect for poison gas prior to 1939; almost everyone assumed urban populations would be massacred with phosgene or another poison gas. Eventually, this didn't keep governments from going to war again (WW2 in Europe was initiated by attacking a small power, after all).
The really bad thing about this is of course that it may be about all too human behaviour and limitations. It may very well be true that humans aren't smart enough to anticipate the nature of modern warfare without practical demonstration in a very similar case. It may also be impossible to keep up respect for war and its horrors for long.
The deterrence value of nukes still depends mostly on references to their devastating use in 1945 and remarks about how modern nukes are many times as powerful and available in sickening numbers. Without this demonstrations mankind would probably not have been able to respect nuclear warfare enough to avert it post-'45.
My own attempts (at ridiculous odds) of making some progress with "reflection" are thus under a very, very sobering omen.