<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 Adolf 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>
what was the main cause of the second world war
Britain and France declaring war on Germany after it invaded Poland in September 1939