What were the main reasons for the failure of the League of Nations?

The League of Nations was a problematic attempt at creating peace in Europe following World War One. It failed for a number of reasons, though some stand out above the rest. The League's aim of world self-determination, disarmament and global diplomacy were ambitious - but failed due to its lack of credibility in that the USA (the largest superpower) was not part of the League, there was no army of the League's own to use to enforce its aims, and its structure which meant that any progress or investigations (for example, the Manchurian Crisis) took too long and meant it was out-of-date.