Like in real combat taking of prisoners of war could be included in the game.
Every time a Unit is about to lose a battle there'd be a chance they would offer to surrender to the victorious unit/army.
You'd need to escort such prisoners to forts, castles or military jail camps. After the conflict is over you could agree to exchange of prisoners, the other nation may pay you to have their prisoners released.
Additional bonus would include capturing of enemy's Great Generals(if these are included in the game) , which could provide a large ransom.
Every time a Unit is about to lose a battle there'd be a chance they would offer to surrender to the victorious unit/army.
You'd need to escort such prisoners to forts, castles or military jail camps. After the conflict is over you could agree to exchange of prisoners, the other nation may pay you to have their prisoners released.
Additional bonus would include capturing of enemy's Great Generals(if these are included in the game) , which could provide a large ransom.