They knew that the Treaty of Versaille (the reconstruction plan for WWI) had lead to another World War since it had angered another country (Germany) and did not wish to anger any other countries and lead to a third World War.
Just to go into greater detail, the treaty made the Germans pay "Reparations" to Britain and France, against the advice of leading economists such as John Maynard Keynes. These reparations devastated the German economy- to put it into perspective, they would be paying back until 1988! This led to the rise of both Fascism and Communism in Germany, of which Hitler and the Nazis triumphed.
