How did events after World War I lead to intolerance?

Because World War I led both directly and indirectly to poverty in European countries and elsewhere after the War, it also led to intolerance.  There's a close link between the two.

When the German economy crashed, it caused widespread misery and economic dislocation.  Unemployment, hunger, and civil strife became common, and crime rose.  In conditions such as that it is easy to look for scapegoats - someone to blame - and Hitler and the Nazi Party, among others, sought to provide the public with that scapegoat.  In that case it was Jews and Communists.