I am no expert. But have read a lot of research.
The bankers and industrialists (B&I’s) that ran Germany had a problem. Parts of Germany were changing to socialism, the first step to communism. This scared the (B&I’s) to death. Russia had just been taken over. And communisms were in England and Mexico along with several other European countries. The (B&I’s) put Hitler in power and thought they had control of Hitler because they held the purse strings, trade and news. Hitler knew this and changed this balance with the night of the long knifes. The (B&I’s) moved to create social upheaval that would cause the people to remove Hitler. This would happen because Germany did not produce enough food to feed its people. And when the people starved, the leader was usually canned. Hitler knew that if he ever lost power that he would be killed for past actions. Hitler had no money to buy food. The only choice he had was to invade Austria and rob the banks. This had to be done fast. Before the banks could move the assets. The (B&I’s) (which Germany was one of the largest before WWI) were building for a war. Again this was for trade. Germany, England and France had colonies around the world. This gave them trade and made them rich. After WWI, Germany’s colonies were taken away. They (B&I’s) wanted them back. Germany was an industrial nation and needed it retail back. And the only way this was going to take place is if Germany was a world power.
Note, once Hitler got in power, his first steps were to control the banking.
The question should not be what started WWII.
Looking back over a longer period of time. You will see that the Great War started in Russia and was a war against communism. And as many great wars of the past have lasted over a hundred years. So has this war. It is still going on today in places like Taiwan, Cuba and China. In a thousand years it will be looked at as one war.

See my response in thread "What started the war?"