What event played a major role in spread of communism and fascism in Europe

Any particular time? I guess the most relevant time for this question is early half of 20th century.

I think the event was first world war and some of its consequences (in many countries the monarchy was abolished so people "experimented" with new political organisatons, in Germany the war brought huge reparations which contributed to the deterioration of their economy)

and the global economic crisis of 1920