The entry of the U.S. into the war.
The U.S. stayed out of WW I until 1917. When the U.S. entered the war, three years after its inception, the balance of power shifted significantly, allowing for the war to be concluded in 1918.
The war ended in a stalemate.
stalemate
From mid 1914 to the beginning of 1918. More or less the entire length of World War I, except for a short time at its beginning and end.
To break the stalemate of the First World War.
The United States entry into the war
The entry of the U.S. into the war.
That it was pointless
Stalemate.
Would you mind reposting your question with a little more information? There was a stalemate in most of World War I, but World War II happened in so many places, that I do not know of the occurence in your question . . .
no one gains or looses ground
8 years
On a Coast Line somewhere
the entry of the U.S. into the war.
They did help break the stalemate.
stalemate