After World War II, much of Europe was devastated and needed to be rebuilt. However the countries had no money because they spent it all during the war. No taxes could be collected because the people were poor and had hardly anything to eat. The United States at this time was the richest nation in the world. Although Russia was an ally during the war against Germany, the relationship changed after the war and it was feared that unless Western Europe rise quickly again, it would fall into communist hands. The United States came up with the Marshall Plan and offered to help the European countries to recover from the effects of the war. Russia and its allies turned down the offer of assistance. The Marshall plan was a success and all the countries who accepted help recovered.
Punish for aggressive acts--the trials were an international means of punishing those involved in violent and unjust acts leading to and during World War II.
German trials in Nuremberg, Germany and Japanese trials in Tokyo, Japan.
Holding the trials in the countries of the Axis Powers demonstrated the power of the Allies over the defeated countries, but also put the leadership on display in their home countries to work as a deterrent for supporters of the defeated governments.
Middle class European societies, North America. The "Allies," that were against Germany and the Soviet Union depending on which time era/war era you are looking at.
I hope this helps!