It is important to emphasize there were myriad causal factors to World War Two, which began in September 1939 when Hitler invaded Poland. The collapse of the League of Nations was arguably a leading factor, as its demise contributed to the fall of Czechslovakia, Austria and Hitler's invasion of Poland in 1939. However, there are two significant other factors that contributed to World War Two. First, the rise of the Nazi party, led by Hitler, in the 1920s and '30s significantly worried the British, especially after Chamberlain's conference in 1938. The ambitions of the Third Reich threatened the peace and stability of Europe, which was already fragile in the years after WW1. Second, the failure of the Treaty of Versailles (1919), following the devastation of WW1, established a power dynamic in Europe, which emphasised the economic fragility of Germany and its ongoing resentment towards the punitive terms of the Versailles Treaty.