World War II was more important than World War I because it had greater consequences and stakes. The war led to the deaths of millions of people and changed the course of world history. In contrast, World War I had fewer casualties, was focused mainly around Europe and the Middle East, and was more a battle between Empires rather than a fight for certain peoples' survival. To put it bluntly, as brutal as WW1 was, no one built camps and factories dedicated to murdering people and using the bodies they didn't roast in ovens as sources of raw materials. As awful as WW1 was, there was no comparable Holocaust.