Final answer:
The nickname of the group that made most decisions at the Paris Peace Conference after World War I was The Big Four: the leaders of the United Kingdom, the United States, France, and Italy.
Step-by-step explanation:
The group that made most decisions at the Paris Peace Conference after World War I was The Big Four. The Big Four consisted of the leaders of the United Kingdom (David Lloyd George), the United States (Woodrow Wilson), France (Georges Clemenceau), and Italy (Vittorio Emanuele Orlando). They played a key role in negotiating the terms of the peace treaty and determining the fate of Germany and other nations involved in the war.