The term "First World War" was already coined in September 1914 and again in 1918. When this was generally accepted is unknown, but likely sometime after US entry into WW2, mirroring the situation from 1914-1918.
http://en.wikipedia.org/wiki/The_Great_War#Cognate_names_for_the_war
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The term First World War was never used during the war. It was considered the War to End All Wars and people hoped it would never happen again. It was called also refered to as the World War, but not WW1.
The first recorded use was in 1933 when The First World War: A Photographic History was published. WW1 wasn't generally used until WW2 began. The term was in use in 1939.
The Great War was, at the time, unique. When the next war started, the names World War One and World War Two were used because World War One was no longer a one-of-a-kind huge multinational war.
Until World War II it was known as the 'Great War'.
First world war. Great war.
The great war
The great war. world war I. the first world war. The war to end all wars.
The Great War was, at the time, unique. When the next war started, the names World War One and World War Two were used because World War One was no longer a one-of-a-kind huge multinational war.
the great war the great war
The Great War
The Great War
Until World War II it was known as the 'Great War'.
First world war. Great war.
World War I. The numeral name was only added after the second world war. And the "great" meant large in magnitude not excellent.
The great war
World War 1 is often also called the Great War. Of course, when it got this name, no one was predicting World War 2.
The great war. world war I. the first world war. The war to end all wars.
The Great War and it was also known as the War to End All Wars, However, after World War II, the Great War was renamed WW1.
It was called the Great War, the war to end all wars