What war was called the "great war"?

It would be "World War I" that was called the "Great War", since before World War II, this had been the only world war, meaning that calling it World War I before then would have been premature. 

The league of nations was found in 1919 to keep peace after world war l.but it failed to prevent world war ll in 1939,so in 1945 the nations of the world set up a new organization,the united state (un).since then, the un has encouraged international cooperation and worked to resolve conflict