Holocaust supervened before nuclear power appeared as the supreme deterring means which has governed internal relations from 1945 to 1991 and who still does in some parts of the world.
Since 1945, war has turned out to be a non-solution to state problems. The first time this was realized was in Korea. The question of war as a solution reached its peak during the Vietnam war: hundreds of diplomats, politicians, teachers, scientists began to realize war was
obsolete, that it wasn't a means any more, as it had been against fascism.
One of the people who realized that, even though he's far from being a pacifist, is Zbigniew Brzezinski. I'll take him as an example of the international community realizing war is no more efficient to solve nation conflicts, because he has written a very clear book where he details some very interesting points about American foreign policy.
The Grand Chessboard, America and the rest of the World, by Zbigniew Brzezinsk, member of Washington Geostrategic Studies Institute and former Presidential counsellor (Carter, if I recall well).
(I think the book is published by Public Press in the US. In France, the publisher is called Bayard Presse. date of 1rst publication: 1997)
BTW I don't know any civilized form of revenge. Revenge is already a primitive concept which has very little to do with civilization.
In brief, war is obsolete. It's used only, as I've already said, by barbaric dictators (such as the one pointed at by
Freedom House) to find some immediate solutions to latent problems that deserve negociating and thoughtful compromises.
There's a distinction to make with civil wars here, esp. the form it knows in former colonies (Africa in particular), but it'd be too complex to fit the post
.