Here is the full list of all 12 The Great War: Western Front achievements.
Win any medal in a Historical Battle
Win any medal in all Historical Battles
Win a full campaign as the Allies
Win a full campaign as the Central Powers
Win the campaign by taking Paris or Kreuznach before November 1918
In the campaign, make it to December 1919 with either faction
Create a really big hole with the Undermining ability
Complete 300 events in the campaign over multiple playthroughs
Cause 1,000 infantry casualties with gas weapons in any game mode
Destroy 100 machine gun or mortar emplacements with bombers in the course of a single campaign with either faction
Play a multiplayer game to completion
Win the highest possible medal for all Historical Battles