From a comment on what victors can do to losers in a war:

Since this is a history site, we should also note that wars of conquest are no longer legal after 1945, so "most of history" no longer applies.

I know that Nazi Germany and Imperial Japan surrendered in 1945, but I'm not aware of international law changing that year. What changes, if any, happened that year?

  • I didn't read that comment in the original post, but if I had I would have disagreed with it on principles. Human history spans millenniums; in that context, "most of history" most assuredly, does apply.
    – CGCampbell
    Dec 21, 2017 at 13:52
  • @CGCampbell You can't read it without its context. The context being, whether the law of nations on conquest for "most of history" is still applicable to a war in 1967, and it most assuredly does not - because this particular aspect of the law changed. It's not about "most of history" in general.
    – Semaphore
    Dec 21, 2017 at 13:54

1 Answer 1


The Nuremburg Principles declared such wars a crime against peace.

The crimes hereinafter set out are punishable as crimes under international law:
(a) Crimes against peace:
(i) Planning, preparation, initiation or waging of a war of aggression or a war in violation of international treaties, agreements or assurances

This was codified by the International Law Commission at the behest of the United Nations General Assembly in 1950 as the Principles of International Law Recognized in the Charter of the Nüremberg Tribunal and in the Judgment of the Tribunal. However, it is based on the activities and findings of the International Military Tribunal between 1945-6, which is itself concerned with the crimes of the Nazis committed up to and including 1945.

Customary international law does not need to be codified, but are instead general principles accepted by the international community. The fact that such rulings were made in 1945 shows that by that point, the international consensus was that aggressive wars are no longer allowed.

Therefore it is accurate to say that international law had changed by 1945. Moreover, this change was at least two decades in the making. A significant previous milestone was the General Treaty for Renunciation of War as an Instrument of National Policy of 1928.

  • When I studied that period, the 'General Treaty for Renunciation of War as an Instrument of National Policy' of 1928 (or 'Kellogg–Briand Pact') was held up as an example of the naivety of those who placed hope in such things, given that this treaty did nothing to stop the invasion of numerous countries in World War II just over a decade later. If your country was in danger of invasion, which would be more use: a strong army, navy & air force, or an assembly of lawyers, judges and law professors brandishing legal opinions "But you JUST CAN'T invade us - its AGAINST INTERNATIONAL LAW!"?
    – Timothy
    Dec 21, 2017 at 19:14
  • @Timothy Renouncing offensive war doesn't stop you from maintaining a strong defensive military. See: Post-war Japan.
    – Semaphore
    Dec 21, 2017 at 19:14

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