Because most of the major countries of the world were involved in the fighting.
the whole war that's why its called world war
The Great War, or the War to end all Wars.
Vietnam was called Vietnam after World War 2.
The First World War ( 1914 to 1918 ) was also called "The Great War " at the time.
It was also called the Great War.
The Great War
World War I was originally called "The Great War" (not the Civil War)
The war in 1914, originally called the Great War, was later called a world war as it was fought by more countries and on a larger scale than any war before.
Because it progressed on to World War 2
it was war against the great countres of the world
World War 1.
At the time it was going on, it was called "The Great War" and "The War to End All Wars". Loosely, after it was over, it was sometimes called "The World War". Once World War II began, it automatically became "World War I".