Here is the full list of all 14 Militia achievements.
Win 100 Matches of Militia
Win 50 Matches of Militia
Reach Rank 10 in Dark World Mode
Reach Rank 10 in Light World mode
Win 10 Matches of Militia
Win a match with a single unit left
Win a practice match
Clear a floor in a single turn
Clear a floor with a single unit left
Destroy 7 enemy units in a single turn
Win 5 Matches in a Row
Finish the Dark World Tutorials
Finish the Light World Tutorials
Win the first tutorial match