Answer:
World War II happened, because Hitler planned an invasion of Poland, a nation which Great Britain and France swore military help if it were attacked by Germany. Hitler invaded Poland on September 1st, 1939, and two days later, World War II began.
Step-by-step explanation:
Germany was in a terrible state of poverty after they lost the first war. That's when Hitler rised to power, promising the people that they would have a great empire, and food. He blamed all of their troubles to the jews, starting to outcast them.