There are a number of differences between World War I and II.
The primary is the origin story.
With World War I, the war broke out because of a complex web of diplomatic and military alliances that were summoned after the assassination of the Arch Duke of the Austro Hungarian Empire. It was further exacerbated by a culture of nationalism throughout Europe.
World War II broke out because of the belligerence of the German Third Reich and its allies.
A nation-state is a state that is based on one nationality. Often, people of the same nationality share their religion too, and sometimes it also serves to differentiate themselves from other nations, such as in the case of the Bosnians, Serbians and Croats.
A shared religion can be something that the majority of the population shares.
