The "Big Three" countries were the United States, Great Britain and Russia. They were called this because they were by far the most important allied players during the war, with Russia and Britain taking on most of the casualties.
they were the United States, Great Britain, and France
Explanation:
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.