More on Genghis Khan II the Marsforming of Earth, the standard Mongol army is 1 light infantry, 3 shortbow units, 2 nomads and 6 Mongol units. Add 8 war elephants from Burma to complete the max 20 units. You can attack with the Mongol army and leave the war elephants for defense because they have the best armor, inside a castle they can withstand a large army with ranged attacks and they are excellent in melee, do not exit castle to combine their armor with your castle defense rating. If they are defeated they take most of the invaders with them which you can retake with the Mongol army. Works well when you are attacking from a territory bordering with two or more territories. When there is only one territory bordering yours take the war elephants with you, tank you very much.
Best combination of offense and defense in the Old World. Remember, war elephants in your castles and Mongol army attacking invaders.