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Assume the following hypothetical scenario:

There are only three relevant nations, two large ones (A, B) both with nuclear weapons sufficient to destroy everyone (MAD) and a smaller one without nuclear weapons (C).

Further suppose that one of the large nations (A) is determined to conquer C (for whatever reason, but it's a strong one). A may or may not be a democracy but in any case there is a very strong will to invade and capture all of C. The army of A shall further be capable of doing that against the will of C.

B is actually on very friendly terms with C and would like for C to remain as it is. B is on much less friendly terms with A, surely less so than with C. People living in B will probably strongly feel for people in C and therefore B would likely try to defend C. Let's further assume that B and C together are more capable in a military sense than A.

Now I wonder if the mutually assured destruction of A and B actually helps A in conquering C or rather hinders A in doing that or is largely neutral in that regard?

Mutually assured destruction means that A and B should hardly go to full scale war with each other, because that would mean the end of the world. In game theory that is described as a Nash equilibrium.

But what does it mean in this scenario here and how does mutually assured destruction change the equation?

Without nuclear weapons: B would defend C, they would be stronger than A, so A would likely be defeated or decide not to attack in the first place.

With nuclear weapons, there are more (contradicting) possibilities:

  • A can tell B to not interfere in its conquest of C or else A would consider that an attack on itself and retaliate. A would basically virtually extend its borders to include C. MAD would mean that B could not attack A, A could successfully conquer C.
  • Or B could tell A that it considers an attack on C an attack on itself and is ready to retaliate. B would basically virtually extends its "protection zone" to include C. MAD would mean that A would not attack C in order to avoid total destruction.
  • Or both A and B both include C in their MAD and nobody knows what happens.

I'm totally confused by all that game theory and that is where I cannot get to any further. I just want to know if MAD means that small, third, non-nuclear weaponized countries are easy prey, even if (bonus question) in principle they could be part of a defense alliance? Would the situation change if B and C would be in a defensive alliance?

My guess is that it's still like a game of chicken in the end, and whoever hangs on to his life less wins. But what confuses me is that basically anything can happen with some reasoning (see above).

This question is very similar to Does a policy of mutually assured destruction favor rogue states? but in this case here I do not assume that A is a rogue state (just somewhat aggressive and wanting to conquer C otherwise equal to B and there are no madmen involved, just rational actors with specific interests) and it's a specific scenario where a third minor nation is to be invaded. So more specific answers might be possible.

I'm not interested in any special cases here, A could be the US, Russia, China (with more nuclear weapons), C could be Ukraine, Poland, Taiwan, Mexico, ...(or any other small country) and B could be the rest of the world combined in each case. If the outcome depends on specific circumstances just explain to me which they are.

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  • 2
    I'm not sure this is suitable for a concise answer.
    – o.m.
    Mar 22 at 16:16
  • @o.m. What do you think is the biggest problem? Maybe I can further limit the scope should it be too large. Or an answer could summarize results and refer to external sources for further reading. To me it seems like a conflict that could reasonably well arise, but I don't want to discuss a specific setting. Maybe I should focus on what political theory would say about this or if such cases have been discussed before and what the outcome was?
    – Trilarion
    Mar 22 at 16:24
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    There are scientists who discuss MAD in terms of countries A and B, but generally they are from A or B and make assumptions about who is who. Game theory informs some strategy, but it isn't sufficient to give an answer without the particulars.
    – o.m.
    Mar 22 at 16:57
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    I've answered, according to my opinion, but it seems foolhardy to aim to distill 50 years of brinkmanship theory in an easily digestible format here. And, again, my answer is only one of possible interpretations - actual results depend on the state actors involved, ideology and psychology, or perceived psychology, of the leaders. Mar 22 at 19:27
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    You are missing a key piece of information in that comment. People don't want to die defending another country regardless of MAD or not. Just look at all the complaints from the past about soldiers dying on foreign soil defending other countries. In general people don't want to see their loved ones dying defending a country across the world that they know little to nothing about and have no connections to. It doesn't matter if there is a chance of all countries getting destroyed due to nuclear weapons or not.
    – Joe W
    Mar 22 at 20:13

2 Answers 2

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(This is assuming effective MAD parity * BTW, not states with minor nuclear assets).

TLDR: All other things being equal, MAD supports aggressive behavior in non-vital areas.

If BigAggressive (A?) wants to attack Small (C) and BigFriendly (B?) wants to help, it can, should it see it in its best interest, in the absence of nukes.

With nukes you have 2 phenomenon:

  • red lines around Bigs attacking each other's territories (to that I will extend umbrella ** zones such as NATO, Warsaw Pact)

  • strong taboos/disincentives towards direct Big-on-Big combat or even the possibility of combat. Solely because of MAD by this point, as, per your question, BigFriendly can otherwise beat BigAggressive.

So, anything that is not explicitly under umbrella is fair game to either Big, should they really, really, see an interest in doing so. You may see proxy wars in non-umbrella areas but otherwise no Big-on-Big will happen. That's not to say other things can't be used to put pressure, such as sanctions, but you won't see Big-on-Big.

Now, you might also see some implicit umbrella areas such as say petroleum-producing areas vital to either side. But the rest can be pushed against by a sufficiently aggressive Big, should it really want to do it.

Taiwan as an example.

The US defense posture assumes Taiwan would be defended. However, if China invaded tomorrow, that support can be assumed to be far from automatic, due to China's 300-odd nukes (vs 5K USA). Yes, it would probably happen, but...

Yet, the US's conventional forces could, at this moment, obliterate China's, especially the forces having to conduct amphibious and naval operations around Taiwan.

And the US has increasing concerns about China (whether or not those concerns are justified has nothing to do with this answer). A casus belli around Taiwan, at this point in time of Chinese-US conventional power ratios would be a rational, if cold-heartedly bloody, calculation by a great power seeing the rise of another.

Absent those nukes, the US would be expected to almost automatically confront China, instead of quite probably, so it seems to me MAD is an enabler for aggressive actions in non-vital areas.

Additionally, there's no further to look than the current motivation for this question, the "special military operation" Russia is carrying out in Ukraine. If NATO wanted to, and they seem to, they could easily boot out Russian troops from Ukraine. Or at least strongly threaten to. They do not, and they've gone on the record saying they would not. Again, MAD in action.

* China has 300 nukes. US has 5K. However, given what nukes can do to large cities and the absence of large scale anti ballistic missile systems, 300 is more than enough to destroy the US, so it is an effective parity.

** umbrella : "anything we consider as a direct attack on our territory or allies". Note that Big country can't just extend "the umbrella" to the whole world, the other Big would flip out or ignore that. I.e. if the US had said we consider a Soviet attack anywhere in the world, on anything, to be a red line then the USSR would have ignored it or instead considered it as a red line of its own ("No, you can't have the entire world"). So those would have been NATO and the Warsaw Pact countries, respectively.

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  • China has 300 nukes but how many of them are capable of being delivered to US cities? Is there an actual threat to the US from those nukes or are they more of a regional threat?
    – Joe W
    Mar 22 at 17:20
  • @JoeW China may have a number of submarine based nuclear missiles as well as a few intercontinental ballistic missiles but it's not clear how many of them could be intercepted. I read somewhere but cannot find the source at the moment that says that simulations ended up with 1-5 nuclear missiles currently coming through if China and the US would have a full scale nuclear exchange.
    – Trilarion
    Mar 22 at 19:45
  • @Trilarion I think you missed the point. When it is said how many nuclear weapons that China has it doesn't account for how many are on short/medium/long range missiles, how many are gravity bombs or in some other form. I would find it highly unlikely that they would be able to target their entire stockpile (if that 300 number is accurate) at the US as some are more for regional defense then global.
    – Joe W
    Mar 22 at 19:57
  • Interesting answer and in principle what I was looking for. Partly difficult to understand because very condensed. Like what means "red" in "implicit red/umbrella areas". Also the example seems to disagree a bit with the TLDR. TLDR says MAD favors aggressive stances, while the Taiwan examples says the US would probably defend Taiwan. And in the middle you say no Big-on-Big but it would still not be clear who blinks first. The TLDR seems to suggest that aggressive stances are more believable in MAD than friendly defense treaty stances. Is that right?
    – Trilarion
    Mar 22 at 19:58
  • @JoeW That's what I meant, Wikipedia says they have only a couple of ICBMs and a few other missiles on submarines that would be able to hit the US directly. And in the article I remember the simulation said that from this only a very small number (1-5) would hit their targets successfully, so that effectively China may not be able to assure total destruction of the US currently.
    – Trilarion
    Mar 22 at 20:01
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Country C should have a military pact with B and host troops will be stationed there. Knowing this, A will not attack C because it leads to MAD.

However, this means that A will be very reluctant to allow any nearby, previously neutral, countries to have military bases of B. Thus, the stable situation is two spheres of influence and proxy conflicts in third world countries.

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