At the close of world war i, three countries were considered the "big three" for diplomatic purposes. who were they?
russia
united states
germany
france
china
great britain

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"

This sentence is true.