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.