Another comment that might be made about world wars is that whereas a third world was a great fear when I was growing up, that fear seems to have receded. Instead, we seem faced with many local conflicts. Perhaps the greatest fear today is that some terrorist group will acquire atomic weapons -- a truly unprecedented situation.
What do you need to know about these wars? The best blanket statement about both wars is that they were caused by countries dissatisfied with the existing international order. These countries wanted more power and, in seeking it, became a danger to the established order, which went to war to stop them.