What Were the Major Reasons Why the Idea of Collective

What were the major reasons why the idea of collective security failed?

A) Because of Europe's fatigue with war following World War I and the U.S.'s return to a policy of isolationism
B) Because of the disintegration of the British Empire and the rise of Russia's power
C) Because of Germany's inability to pay reparations and the rise of Russia's power
D) Because of the U.S.'s return to a policy of isolationism and the disintegration of the British Empire