Let's talk about just how destructive nukes are, because I think most people grossly underestimate this. One bomb in Hiroshima killed hundreds of thousands. And that was a
tiny little bomb relative to modern standards - 16kt of yield in a mid-sized city of ~350k people. Modern tactical weapons (weapons intended for battlefield use) can have yields exceeding 100kt. Strategic weapons (weapons intended to end other civilizations) go into the thousands of kt. The strongest weapon ever tested being "Tsar Bomba" which had a yield of 55,000kt, so a few thousand times greater yield than the Hiroshima nuke - which was by itself enough to instantly destroy a mid-sized city and kill more than 40% of its population.
I think it's easy to lose scale/context when looking at things like nuclear test footage, so let's go the other direction. This [1] is the "Mother of All Bombs / MOAB / GBU-43" that was detonated in Afghanistan. It's the second largest conventional weapon ever fielded, weighing more than 20,000lbs and and 30+ft long (so that little blip on the screen is 30 ft for scale). It had a yield of 0.01kt. So now imagine something with literally hundreds of thousands of times greater yield - that's a modern nuke. Or, if it helps for visualization purposes, imagine hundreds of thousands of those raining down - same net effect.
So if nuclear war ever breaks out it's not going to be countries using their nukes to target isolated (and nuclear fortified) launch silos and bunkers in the middle of nowhere - they're going to try to destroy the other country (targeting things like population, economic, health, agriculture), so that they can completely eliminate the threat. And suffice to say - it won't take many nukes. The only reason you'd have thousands is to overwhelm any sort of future-tech missile defense systems as well as to eliminate any possibility for an effective first strike attack attack against you. Although even the nukes themselves are also designed to deal with missile defenses, with one missile often breaking up into multiple independent warheads on approach. This also maximizes the damage for reasons outside the scope of the post.
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So the point of this is that thousands of nukes is already enough to basically destroy every single major city in the world and thus destroy basically every single country in the world. There's no scenario where suddenly you need to scale up to tens of thousands of nukes or whatever. In fact nations like North Korea already clearly have an effective deterrent with a stockpile that's in the tens of missiles.
[1] - https://www.youtube.com/watch?v=Q6rSxJnpGNg
