Is this a sentence fragment?
By the time the Guerra Bianca, or White War, ended in 1917, Italian and Austro-Hungarian soldiers fighting for three years in extreme conditions at altitudes of up to twelve thousand feet.
A: no
B: yes
This is a sentence fragment. It does not express a complete thought.
By the time the Guerra Bianca, or White War, ended in 1917, Italian and Austro-Hungarian soldiers fighting for three years in extreme conditions at altitudes of up to twelve thousand feet.
Here is one way to fix the sentence fragment:
By the time the Guerra Bianca, or White War, ended in 1917, Italian and Austro-Hungarian soldiers had been fighting for three years in extreme conditions at altitudes of up to twelve thousand feet.