Here is the full list of all 20 Middle Age Conquest achievements.
Reach 100 K Army Power
Have 100 Houses
Win A Fight
Reach 50 K Army Power
Finish The Third Age
Reach 10 K Army Power
Lose A Fight
Go to War Once
Finish The Second Age
Have 50 Houses
Get 100 Research Points
Have 50 Wood Worker
Have 50 Gold Worker
Have 50 Food Worker
Trade Any Resource For Another
Finish The First Age
Go Fightzone Once
Upgrade The Blacksmith For Once
Have 10 Houses
Let's Find A Chest Full of It