From what I understand, pre-WWII wars were usually resolved by the losing leaders either being sent into exile or immediately murdered by the winning army. Why was the aftermath of WWII so different?
When a war is set between two sides, there are rules and regulations conducted by conventions and corporations such as The Geneva Convention, UN, Red Cross, et cetera. They make sure that war is in a civilized boundaries and crimes against humanity are not broken (e.g. Chemical Warfare and treatment of POWs). During WWII, many Japanese and German officers mandated and partook in crimes against humanity. The holocaust, massacres, chemical experimentations, etc.
The point of setting these rules and conferences is to keep humanity at a certain set of morals and understanding compassion to one another. Just putting them up against a wall and shooting them without a trial to bring their crimes to the light and charging them for it is against the point of all the rules set in place in the first place. Even though the result is the same, committing an act like this doesn't separate the winning side from killing merciless or in a more humane light.
Actually, things like this were done after wars. For example, there was an International Tribunal after World War I in Paris to convict all those who committed violations of war. It was called the Leipzig War Crime Trials. It was an outrage to many countries because only Germans were being convicted, some seemed biased and it never got a true spectrum of the war of which sides actually committed violations.
From a source of the significance of the tribunal/Nuremburg Trials:
The Nuremberg Trials have had a great impact on international law as a whole. Crime against humanity was given a legal definition. For the first time in history, the pre-eminence of individual rights and their being subject to codified law was established, in an area which hitherto only recognized the rights of States. Fundamental principles which emanated from the Nuremberg Trials include individual responsibility for international crimes, the right of the Accused to a fair trial, the historic declaration whereby the position of a Head of State or a high level government official, does not guarantee immunity and finally, respect for human rights principles which have now become universal.
I hope this helped.
Here are my sources:
My first post mods, please tell me I did everything right. Go easy on me haha