How did the worldwide effects of the Great Depression cause World War II?
There are at least two ways in which the effects of the Great Depression helped cause WWII. First, they helped lay the foundation for the rise of fascism/Nazism in Germany and of militarism in Japan. Secondly, they devastated the economies of the US, France, and the UK. This caused those countries to be preoccupied with domestic economic issues and less interested in foreign affairs.
The Great Depression caused great harm to economies around the world. In some countries, the economic harm led people to accept political radicals because they were desperate for someone to fix their economic troubles. In Germany, this meant that people were willing to support the Nazis. In Japan, people supported more militaristic politicians. In both cases, these new leaders brought their countries into war.
Even in countries that did not become radicalized, the Great Depression had a significant impact. Politicians in the US, Great Britain, and France stopped worrying so much about foreign affairs and focused almost solely on trying to improve their own economies. This meant they were willing to let Germany and Japan get away with aggressive actions such as the German rearmament and the Japanese incursions into China. These governments looked the other way, allowing Germany and Japan to get stronger to the point where they were ready to go to war.
The effects of the Great Depression, then, brought war-hngry leaders to power in Germany and Japan and caused leaders in the US, France, and Britain to ignore Japanese and German aggression until it was too late.