Here is the full list of all 20 Field of Glory II: Medieval achievements.
You won your first battle!
Won a battle on Baron difficulty
Won a battle on Duke difficulty
Won a battle on Prince difficulty
Won a battle on King difficulty
Created a Multiplayer challenge
Won a Multiplayer battle
Fought a losing Multiplayer battle to completion without conceding
Won a campaign
Won a 15 battle campaign
Made an enemy unit autodrop cohesion from a flank charge
Passed a cohesion test when only double six would have passed
Suffered a double cohesion drop which could only occur on a roll of snake eyes
Killed an enemy C-in-C
Rallied a routing unit with a general
Made a unit drop cohesion from artillery fire
Destroyed an enemy banner wagon
Routed mounted knights with peasants
Won a battle with a Baltic or Lithuanian army against the Teutonic Order on at least Baron difficulty
Won a battle with a Mongol or Tatar army on at least Baron difficulty