In the past few centuries an unwritten rule has been followed where countries make up some sort of plausible-sounding excuse before starting a war. As an example, Hitler invaded Czechoslovakia in 1939 because he "wanted to protect the Sudeten Germans". Likewise World War I officially began because of the assassination of Archduke Franz Ferdinand.

But when did this practice first begin? When did it become necessary to somehow rationalize the use of force?

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    Slightly opinion related... "making up excuses" - is it your assertion that the use of force requires no justification? You'd be out in a lonely corner of humanity if that is true...Pretty much every society in existence requires justification before it starts spending the lives of its citizens.
    – MCW
    Commented Jun 19, 2017 at 17:44
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    The Romans certainly did it; I suspect it goes back as far as recorded history.
    – antlersoft
    Commented Jun 19, 2017 at 18:02
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    Even before notions of "international community" didn't exist, countries still need to justify for their own citizens...even in autocracies, a "just war" improves moral. I believe Sun Tze talks about this in the Art of War, and that's a work from the 5th century BC.
    – user15620
    Commented Jun 19, 2017 at 18:26
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    I assume ever since we had the communicative facility to say: "That guy there, he's looking at your girl."
    – Jae Carr
    Commented Jun 19, 2017 at 22:05
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    Who says that the reasons given (though your list seems to have disappeared) are in fact always pretexts, and not the actual reasons?
    – jamesqf
    Commented Jun 20, 2017 at 5:49

1 Answer 1


I think it has always been done, e.g., 3,000 years ago Greeks justified a war by a kidnapping allegation.

Justification of war is important for one's own troop and population morale, so the theoretical framework has been around for millennia.

Paraphrasing @SPavel, "your people are unlikely to risk their lives just because you are bored, or greedy, or horny".

Note that this does not mean that the justification has to be fake. If your group (tribe, city, state, nation, empire) is starving, waging a war for resources is likely to sound reasonable to your people.

The bottom line is that the war pretext exists first and foremost for internal consumption. (Here internal may include allies).

A secondary reason is actually getting more and more important with the development of civilization and diplomacy: avoid war in the future. A party which, first, clearly states the reasons for war, and, second, sticks to them (i.e., goes to war if and only if certain conditions are satisfied), may be less likely to find itself faced with war (depending on how reasonable the conditions sound to the neighbors and how reasonable those neighbors are themselves).

Regarding this secondary reason and avoiding war in the future in general, please see the Nobel lecture aptly named War and Peace by Robert Aumann - a genius game theorist.

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    Indeed. Your citizens are much less likely to lay down their lives if the stated reason is "the king is bored".
    – SPavel
    Commented Jun 19, 2017 at 19:29
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    ... or just greedy, or horny or ...
    – sds
    Commented Jun 19, 2017 at 19:31
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    This is a good answer to the first half of the question, but I was hoping for an answer to the other part: When did it become necessary to somehow rationalize the use of force? (emphasis added)
    – Charles
    Commented Jun 20, 2017 at 3:51
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    @jamesqf Just like Jonathan said above, a lot of wars were just naked attempts to steal resources, people, and land. Today these are never given as reasons, there is always some other pretext. In either case the use of force had that ugly but 'rational' motive, but at some point the idea of having a veneer of respectability went from "nice to have" to obligatory, and I think the question asks about that point in addition to the simpler question of how long has it been done at all.
    – Charles
    Commented Jun 20, 2017 at 6:24
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    @Charles I think you're going to have a hard time finding a specific point in time. I suspect that one important tipping point is the development of formal military alliances. 'Moar resources!' can easily be sold to your own populace as a valid reason, but if you have an ally who might come to your aid only because you signed a paper 3 years ago, then he's going to need a justification for his people too.
    – Falc
    Commented Jun 20, 2017 at 9:04

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