Question

At the close of World War I, three countries were considered the "Big Three" for diplomatic purposes. Who were they?

Answer 1

The Big Three were the most powerful of the Allies, and the leaders of the group. They determined the policies and  the actions of the Allies.

Those were:

United States, Great Britain and Soviet Union

Together with China, they were also called "The Big Four"

Answer 2

The "Big Three" for the purposes of diplomatic activity in the promotion of peace after the First World War were United States, Great Britain and France, which was also the Big Four with Italy. The Big Three was composed of Woodrow Wilson of the United States, David Lloyd George of the United Kingdom, and Georges Clemenceau of France, together with Vittorio Emanuele Orlando of Italy as a Big Four. Russia (Soviet Union) was busy with the issues of implementing the Revolution in reality, as well as with the problems of the civil war that arose after the Revolution that lasted even after the WWI, the problem of transformation of the economy, etc.