SpeakerA."We must take action even if we are not sure it will work. To do nothing to stop them would be a repeat of the Munich mistake."
SpeakerB."We must recognize the increasing interdependence of nations and join the United Nations."
SpeakerC."Stopping the spread of communism can and must take several forms. We must be willing to do whatever is necessary."
SpeakerD."Involvement in European affairs would be a mistake. We should not jeopardize our peace and prosperity over issues that Europe's ambitions and rivalries control."

The "Munich mistake" mentioned by speaker
A refers to a policy of ______________