This thought experiment has been regularly used as an introduction to the theory of realism in international relations. Realism, at least how it was originally understood (today there are many flavours of realism), is that nation states ought to go to war only when it serves the nation’s interest to do so. Moral arguments are irrelevant.
The thought experiment is an imagined discussion between the Athenians and the Melians, called ‘the Melian dialogue’. This was based on the actual historical event where Athens laid seige to Melos, and the Melians were easily defeated due to Athens having a much more powerful army.
J. Baylis et al (2017) explain that the dialogue is the Athenians attempting to persuade the Melians to submit without resistance, and provide the following exerpt of the dialogue:
“ATHENIANS: Then we on our side will use no fine phrases saying, for example, that we have a right to our empire because we defeated the Persians…you know as well as we do that, when these matters are discussed by practical people, the standard of justice depends on the equality of power to compel and that in fact the strong do what they have the power to do and the weak accept what they have to accept.
MELIANS:…you should not destroy a principle that is to the general good of all men-namely, that in the case of all who fall into danger there should be such a thing as fair play and just dealing…
ATHENIANS: This is no fair fight, with honour on one side and shame on the other. It is rather a question of saving your lives and not resisting those who are far too strong for you.
MELIANS: It is difficult…for us to oppose your power and fortune…Nevertheless we trust that the gods will give us fortune as good as yours…
ATHENIANS: Our opinion of the gods and our knowledge of men lead us to conclude that it is a general and necessary law of nature to rule whatever one can. This is not a law that we made ourselves, nor were we the first to act upon it when it was made. We found it already in existence, and we shall leave it to exist forever among those who come after us. We are merely acting in accordance with it, and we know that you or anybody else with the same power as ours would be acting in precisely the same way…You seem to forget that if one follows one’s self-interest one wants to be safe, whereas the path of justice and honour involves one in danger…This is the safe rule-to stand up to one’s equals, to behave with deference to one’s superiors, and to treat one’s inferiors with moderation.
MELIANS: Our decision, Athenians, is just the same as it was at first. We are not prepared to give up in a short moment the liberty which our city has enjoyed for 700 years.
ATHENIANS:…you seem to us…to see uncertainties as realities, simply because you would like them to be so.”
The questions Baylis et al (2017) asks us from this thought experiment are:
Does power always trump moral principles?
Who were right? The Athenians or the Melians?
If you want learn more about International Relations, John Baylis, Steve Smith and Patricia Owens have a great introductory book called “The globalization of world politics: An introduction to International Relations”.