According to international law, when is first-use nuclear strike justified?


Hong Kong (CNN) — Military planners in Washington pushed for the White House to prepare plans to use nuclear weapons against mainland China during the Taiwan Strait crisis in 1958, newly leaked documents appear to confirm.

The documents, first reported on by the New York Times Saturday, reveal the extent of Washington's discussions about using nuclear weapons to deter a Chinese invasion of Taiwan, including the acceptance by some US military leaders of possible retaliatory nuclear strikes on US bases.

The U.S. was willing to use nuclear weapons against China to deter and not in response to an invasion, but this strikes me as weird because you would think there are international laws that would prevent such a rash action. Am I wrong? Do we have new laws that would deter such an action?

  • 23
    "you would think there are international laws that blah blah blah". Why do people put so much faith, trust, hope and love in something as toothless as "international law"?
    – RonJohn
    Commented May 31, 2021 at 3:13
  • 1
    With a large enough military you can enforce any law you want.
    – acpilot
    Commented Jun 1, 2021 at 4:30
  • There is a saying among states angatonized by the US: "When America says you have nukes, you better really do have nukes."
    – Faito Dayo
    Commented Nov 13, 2023 at 16:08

4 Answers 4


Frame challenge, mostly motivated by:

The U.S. was willing to use nuclear weapon against China to deter and not in response to an invasion, but this strikes me as weird because you would think there are international laws that would prevent such a rash action.

You are perhaps giving too much weight to "international law". Yes, there are legal agreements that nations agree to abide by, but in the last analysis, nations are fully sovereign until they are coerced by force of arms or by sanctions to change their behavior.

If this was not the case, little peccadilloes like the 2003 Iraq invasion (US), ongoing occupation of Palestine (Israel), Uyghur persecution (China), occupation of Diego Garcia (UK), annexation of Crimea (Russia) would never have happened.

Oh, but these are powerful nations, you say? I give you the Rohingya (Myanmar).

In the case of US, China, France, UK, Russia, international law, via the UN, is even less of a bother as these 5 have veto powers.

On to the actual circumstances.

After WW2, while it had a nuclear monopoly, the US was not averse to waving a nuclear bully stick to get others to stay in line. I am posting this 16 Nuclear Crises of the Cold War, because it seems to sum up a good deal of them, but it is quite possible the information is biased against the US (think Chomsky). Still, something to chew on.

The fact that the Soviet and Mao Communist system were evil and needed to be resisted? Very relevant, but that nuclear coercion still took place nevertheless.

Now, in 1958, the USA had just gotten out of the Korean War, a war of aggression freely started by North Korea in 1950. NK's efforts quickly collapsed and the war then was equally freely chosen to be continued by PRC on North Korean territory. This war was savage, often involved maltreatment of prisoners (by both sides, but largely a Communist activity). It was cease-fired for reasons of mutual exhaustion by both principals (i.e. USA and PRC) in 1953. The US learned that China had endless sources of soldiers and was not at all averse to wasting their lives (Chang and Halliday claim Mao used the war to conveniently get rid of undesirables).

This is the context you are looking at. At that point, the US still, as it would show during the Cuban crisis of 1962, very much in nuclear coercion mode whenever it felt it could get away with it.

Over time, nuclear war has become less and less acceptable, both for risk limitation reasons (i.e. not blowing up the whole planet), for reasons of military effectiveness (some studies made during the Vietnam War doubted the US could win it by nuking) and, hopefully ethics (or the desire not to look bad).

What "international law" had to say in 1958 probably was very secondary to the second and third consideration, military advantages and not looking too bad.

In 2021? "International law" would still probably be very secondary to the general revulsion first use would draw on the country doing it, unless, maybe, if they were at threat of annihilation.

Still, first use is a useful bit of ambiguity to leave in play, especially if you want to avoid nuclear wars happening. Take two nations, A and B, both being nuclear, but B has the edge in conventional forces. If A is coy about not renouncing first use, B has to factor in that attacking A may very well result in nuclear strikes. This can dissuade B from trying to defeat A conventionally and then ultimately causing A to launch. So both remain quiet.

For A and B, read NATO vs USSR during the Cold War in Western Europe. Or Pakistan and India nowadays. Best to stay away from "let's try a good old conventional war because first use is against international law".

Of course, given a long enough period of time, low-probability events will eventually happen and that's why nuclear weapons, even if they've so far managed to stop a conventional WW3 from happening, are a long term risk for mankind.

Finally, note that just because some in the US military presented the president with an option, the president didn't in fact take that choice, so your question does not, quite, have the moral significance you seem to imply.

(As far as what international law actually has to say, I'd be surprised if it didn't condemn first use under most conceivable scenarios and I defer to @meriton 's answer).

  • There's also a socially and morally important dimension to degree of use in a first-use situation. Often when people read 'we will use nuclear weapons in response to XYZ', they're imagining a volley of ICBMs - the most extreme escalation possible. While any use of nuclear weapons would be a massive escalation and likely draw criticism, use of tactical weapons in friendly territory or international waters is categorically different from strategic strikes on the civilian population. Commented Jul 19, 2023 at 20:05

Any use of nuclear weapons is very likely to violate international law. Specifically, article 51 of "Protocol Additional to the Geneva Convention", which writes:

  1. Indiscriminate attacks are prohibited. Indiscriminate attacks are:

    • those which are not directed at a specific military objective;
    • those which employ a method or means of combat which cannot be directed at a specific military objective; or
    • those which employ a method or means of combat the effects of which cannot be limited as required by this Protocol;

    and consequently, in each such case, are of a nature to strike military objectives and civilians or civilian objects without distinction,

  2. Among others, the following types of attacks are to be considered as indiscriminate:

    • an attack by bombardment by any methods or means which treats as a single military objective a number of clearly separated and distinct military objectives located in a city, town, village or other area containing a similar concentration of civilians or civilian objects; and
    • an attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated.

This international treaty has been ratified by 174 nations, including the nuclear powers of Russia, China, the UK, and France. It has been signed, but not ratified by, the United States, Iran, and Pakistan.

Note: Hiroshima and Nagasaki, as well as the numerous indiscriminate attacks carried out by conventional means during WWII, occurred before this treaty was written.

The International Court of Justice, in the landmark case "Legality of the Threat or Use of Nuclear Weapons" (1996), held:

The threat or use of nuclear weapons would generally be contrary to the rules of international law applicable in armed conflict, and in particular the principles and rules of humanitarian law; However, in view of the current state of international law, and of the elements of fact at its disposal, the Court cannot conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defence, in which the very survival of a State would be at stake.

That is, the ICJ held that use of nuclear weapons is generally illegal, and may possibly be legal only in "extreme circumstances of self-defence, in which the very survival of a State would be at stake".

In its written opinion, the court elaborated:

Thus, methods and means of warfare, which would preclude any distinction between civilian and military targets, or which would result in unnecessary suffering to combatants, are prohibited.

In view of the unique characteristics of nuclear weapons [...], the use of such weapons in fact seems scarcely reconcilable with respect for such requirements.

Nevertheless, the Court considers that it does not have sufficient elements to enable it to conclude with certainty that the use of nuclear weapons would necessarily be at variance with the principles and rules of law applicable in armed conflict in any circumstance.

  • I don't think this is a valid reading of the treaty. The first bullet point of section 5 will be hard with nukes, but attacks on military targets can be made even if it is likely that there will be collateral damage.
    – o.m.
    Commented May 29, 2021 at 16:42
  • It's not that simple. For an overview of the considerations involved, you may want to read the paper Nuclear Weapons and international humanitarian law by the International Committee of the Red Cross.
    – meriton
    Commented May 29, 2021 at 17:22
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    The paper contains the section "There are serious questions as to whether nuclear weapons can be used in accordance with these essential IHL rules." I agree with the "serious questions" assessment. But saying that "any use" violates international law, as you do, goes beyond that.
    – o.m.
    Commented May 29, 2021 at 17:40
  • The paper also quotes the ICJ with "The Court would observe that none of the States advocating the legality of the use of nuclear weapons under certain circumstances, including the ‘clean’ use of smaller, low yield, tactical nuclear weapons, has indicated what, supposing such limited use were feasible, would be the precise circumstances justifying such use;", and in its opinion, that "the use of nuclear weapons seems scarcely reconcilable" with legal requirements. Nevertheless, as the court shied away from a summary judgement, so shall I, and I have thus added a "very likely" qualifier.
    – meriton
    Commented May 29, 2021 at 18:52
  • Also note that a document which is not ratified by the united states is a pretty flimsy binding on the united states, even by the unimpressive standards of international law. Commented Jul 14, 2023 at 17:01

The U.S. shot a live nuclear missile a thousand miles in 1962

The Frigate Bird test (part of Operation Dominic) involved a missile travelling 1000 nautical miles to a site "480 nm ENE of Christmas Island", give or take 30 miles. The test remains an obscure footnote to history. From this I think we can rule out the idea that international law would have restricted the use of nuclear weapons per se in 1958. Their use to target civilians would have drawn some opposition, but 1958 was just 13 years after Hiroshima and Nagasaki. I assume targeting naval forces would have been less controversial. The main deterrent against starting a nuclear world war was never the risk of a proceeding in the Hague!

  • The war itself must be justified. That means either a defensive war (including preemptive war) or some other valid reason. Evaluating this will be a decision of the other governments, driven at least as much from politics as law.
  • Within the war, the nuclear strike must meet the requirements for the use of military force: distinction, proportionality, military necessity.
    That means targeting an arms factory in a city might be legitimate, targeting the housing next to it isn't, even if this makes zero difference with a megaton strike and the inaccuracy of the delivery system.
    Proportionality will be very hard to explain, but perhaps not impossible.

And let me note that your questions seem to indicate a misunderstanding of the nature of international law.

Countries are assumed to be sovereign. Western thought goes further in saying that the sovereignty rests in the will of the people, expressed through democratic elections. But that isn't universally accepted, even if lip service to democracy is fashionable these days.

Within a country, citizens are required to obey the rules set by their legislature. Anything else would be an act of revolution or rebellion. Revolution may be morally permitted, even morally imperative, but that does not make it legally permitted. Revolutionaries are gambling that when the dust settles, the new government will consider them heroes.

On the global level, the United Nations does not have the nature of a world parliament which can pass laws affecting all countries. What you have instead are:

  • Customary international law. There are not many precedents for nuclear use.
  • International treaties. These are voluntarily signed by the nations, and usually they have a means to leave again.
  • The raw power of the UNSC. This represents the victors of WWII, with the PRC having replaced the ROC and Russia having replaced the Soviet Union. They wrote into their charter that they can make binding decisions for the rest of the world, but at the time they wrote it there was no precedent to allow that. One could argue that the last three quarters of a century created such a precedent.
  • Hitting an arms factory in a populated area with a nuclear weapon in the megaton range is a war crime. For a use of force to be legal, civilian collateral damage must be in proportion with the military objective to be achieved, and leveling much of a city to take out one factory is disproportionate in the extreme.
    – meriton
    Commented May 30, 2021 at 1:01
  • @meriton, depends on the size and the hardening of the factory. I wrote that proportionality would be very hard to explain, in bold letters.
    – o.m.
    Commented May 30, 2021 at 4:08
  • A 1 megaton warhead at standard detonation height destroys most buildings in a range of 6 kilometers, and causes 3rd degree burns out to 12 kilometers from ground zero. That's one huge factory! I thus agree that proportionality is very hard to justify. What prompted my comment was the phrasing "targeting a factory might be ok, but targeting the housing nearby isn't, even if this makes zero difference with a megaton strike", which I took to mean that the size of the blast zone may be ignored when assessing the legality of the target. I now realize this was not your intent.
    – meriton
    Commented May 30, 2021 at 13:16
  • @meriton, yes. Targeting the housing would be a crime, accepting it as collateral damage would be a (hard to justfy) question of proportionality.
    – o.m.
    Commented May 30, 2021 at 13:41

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