(A) They were isoloationist
(B) They were too busy dealing with the Bolsheviks
(C) ** Britain and France didn’t want communist Russia to join
(D) If America were not in, they did not want to join either
EXPLANATIONS BELOW
Concept note-1: -Russia had fought as one of the Allies until December 1917, when its new Bolshevik Government withdrew from the war. The Allied Powers refused to recognize the new Bolshevik Government and thus did not invite its representatives to the Peace Conference .
Concept note-2: -The Soviet Union is expelled from the League of Nations following the pact with Germany and aggression against Finland. The Soviet Union only became a member of the League of Nations in 1934, a year after Germany left, and was expelled from the League on 14 December 1939 for aggression against Finland.
Concept note-3: -The reason why Britain didn’t declare war on the Soviet Union is an intriguing one. Unknown to the general public there was a ‘secret protocol’ to the 1939 Anglo-Polish treaty that specifically limited the British obligation to protect Poland to ‘aggression’ from Germany.
Concept note-4: -Despite formulating the concept and signing the Covenant, the United States never joined the League of Nations, and some relatively-isolated sovereign states in Asia also did not join, including Saudi Arabia, Yemen, Mongolia, Nepal, and Bhutan.
Concept note-5: -September 18, 1934 general meeting of the League of Nations adopted a resolution on the admission of the USSR into the League and the inclusion of its representative to its Board as a permanent member.