What is needed to create a World War? What would create one today? Is it even possible?

Something that is needed to create a World War is a cause. Something that a lot of countries are will to fight for. Lots of countries aren't all way willing but mostly the main ones join in to help out. Something that could create a World War today would be over oil. Oil is something that everyone needs. So if a War breaks out over oil it would be a big war with lots of countries. It might be possible to start a World War today but you never know what will happen.