Here is the full list of all 12 War Theatre: Blood of Winter achievements.
Destroy three units in one turn.
Destroy four units in one turn.
Destroy five units in one turn.
Defeat the AI in a Skirmish game.
Complete one quest.
Complete five quests.
Complete ten quests.
Purchase one perk.
Purchase five perks.
Purchase ten perks.
Obtain 10000 gold from career quest rewards.
Obtain 25000 gold from career quest rewards.