Although World War I and World War II are closely related, I do not agree that it is fair to consider the two of them to be the same conflict. To a certain extent, the two conflicts shared some characteristics, some causes, and some ideas. Nevertheless, after WWI was concluded, a peace treaty was signed. The Treaty of Versailles was signed on 28 June 1919, and it put an end to World War I. This was signed by Germany and the Allied Powers and registered by the Secretariat of the League of Nations.
Someone who disagrees with this statement might claim that Germany's aspirations were catalysts during both wars. While this is true, I do not think it warrants treating both wars as one, as Germany's ambitions took very a very different form in each one. Moreover, the racist and eugenic theories that dominated the second war were not particularly relevant in the first one.