<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Some long - term causes of World War II are found in the conditions preceding World War I and seen as common for both World Wars . Supporters of this view paraphrase Carl von Clausewitz: World War II was a continuation of World War I by the same means . In fact, World Wars had been expected before Benito Mussolini and Adolf Hitler came to power and Japan invaded China . </P> <P> Among the causes of World War II were Italian fascism in the 1920s, Japanese militarism and invasion of China in the 1930s, and especially the political takeover in 1933 of Germany by Hitler and his Nazi Party and its aggressive foreign policy . The immediate cause was Britain and France declaring war on Germany after it invaded Poland in September 1939 . </P> <P> Problems arose in Weimar Germany that experienced strong currents of revanchism after the Treaty of Versailles that concluded its defeat in World War I in 1918 . Dissatisfactions of treaty provisions included the demilitarization of the Rhineland, the prohibition of unification with Austria (including the Sudetenland) and the loss of German - speaking territories such as Danzig and Eupen - Malmedy despite Wilson's Fourteen Points, the limitations on the Reichswehr making it a token military force, the war - guilt clause, and last but not least the heavy tribute that Germany had to pay in the form of war reparations, which became an unbearable burden after the Great Depression . The most serious internal cause in Germany was the instability of the political system, as large sectors of politically active Germans rejected the legitimacy of the Weimar Republic . </P>

What were two major causes of world war 2