Why did the Western powers follow the policy of appeasement during the Second World War?

The belief behind appeasement was done to avoid another calamity such as the First World War.  Leaders such as Chamberlain of England were convinced that the atrocities of the First World War should be avoided at all costs.  Reeling in from the chaos and undermining of faith, Europe was shattered in  geographic, financial, and emotional terms.  All nations felt to a certain extent that the paradigm with which they viewed the world at the start of the conflict was severely undermined by it.  The policy of appeasement struck at this very essence for it sought to avoid war at all costs.  If this meant dealing with terms articulated by Hitler at the time, it was seen as a needed sacrifice.  At the time, Hitler was not seen as the universal symbol of threatening evil that he is seen as now.  The belief was that containing him was an acceptable risk if it prevented another entry into widened conflict.  Bearing this in mind, it became nearly impossible to stop him when all leaders realized the existential threat he posed.  This would mean that the policy of appeasement, a hope to avoid war, actually had much to do with a new one starting.