In: Economics
World war never happened because of nationalism but it was lead by nationalists who think their country is greater than other. The main reason for World War I is the camps that are formed in Europe where the supporters of Germany took one side and supporters of France took the other side which lead them to fight against each to have the authority on every part of Europe. World War I is just about land which give them power of the entire Europe and make them the Emperor and the most powerful man in this world.
Some mistakes done by Germany in WWI lead to fall of Europe in that war and made them to take blame for war whichlead them to sign Versailles treaty. The thing which lead to WWII is not only this treaty agreement but it is one of the reason. In this agreement everything that Germany owns were taken and made sure that they are like slaves to remaining countries in world. This treaty gave Hitler the motivation and anger to wage war on all powerful nations in the world and it made him to kill many people in name of Nationalism.
Treaty is not the reason for war but gave motivation some one to become a psychopath and lead to another devasting chaos which cannot be forgotten.