Why were the peoples of Europe so eager to believe that peace was possible through such acts as the Kellogg-Briand pact and the agreements at Locarno? What was wrong with such ideas?

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Why were the peoples of Europe so eager to believe that peace was possible through such acts as the Kellogg-Briand pact and the agreements at Locarno? What was wrong with such ideas?
*underline thesis statement.