Originally Posted by norbici
How about Heroes having the ability to capture enemy units after battle taking them hostage and asking a ransom for them(in money or resources), from the enemy player. But if the captured units are from the same race as u, after the ransom expires u can keep them and use them in your own army. Same with the mercenary units that u will encounter during quests or raiding, for example after u killed the majority of the mobs u could have 3 options: Exterminate enemy, Let them flee or Capture/Enslave enemy and take them home where u can use them after a while.
Sounds similar to Total War's system of surrendering units... and we have discussed this in another topic where we debated the use of morale and possibly defection/surrender of units