(A) ** Non-members could just ignore the sanctions.
(B) ** Members who were sanctioned could just trade with non-members.
(C) There was not enough trade after WWI for sanctions to work.
(D) ** The League could not use force to carry out the sanctions.
EXPLANATIONS BELOW
Concept note-1: -The failures of the League in the 1930s were not only because of aggressor nations undermining its authority, but also down to its own members. Britain and France, the two most influential members, ignored the League in their efforts to appease Hitler-actions that arguably led to the outbreak of the Second World War.
Concept note-2: -The League of Nations was formed to prevent a repetition of the First World War, but within two decades this effort failed. Economic depression, renewed nationalism, weakened successor states, and feelings of humiliation (particularly in Germany) eventually contributed to World War II.
Concept note-3: -The League failed to bring about disarmament and also to solve several problems. These failures included: Vilna, 1920, Russo-Polish War 1920-21, Greece vs. Turkey 1920-21, Memel 1923, the occupation of Ruhr 1923, Corfu Incident 1923. The League often failed to carry the self-determination policy out.
Concept note-4: -Disarmament talks failed, because Germany demanded as many weapons as everyone else. The League sent economics experts to help Austria when its government went bankrupt. Greece obeyed the League’s orders to pull out of Bulgaria in 1925.