What Creates a World War? What Would Create One Today?

I think anything can create a World War. The most popular would probably seem to be jealousy. For example, America has freedom and things a lot of countries don't have. Other Leaders could be very jealous, causing anger towards America. Countries could try to tear us down to feel powerful causing our allies to get involved. right there, a war is created. I feel like then all other countries get involved because of past grudges or to help their surrounding countries.