World war 1 was a war of anger that had been brewing for a while. It started with the assassination of Franz Ferdinand, an Austrian Duke. And escalated as countries were pulled in thanks to the web of Allies. Was fought in trenches.
Meanwhile world war 2 was Hitlers grab for power and hate of the Jews. This went against many countries morals so they stood up. And the Japanese bombed Pearl Harbor bring in the USA. Was fought using new military invasion tactic.