A Druzhinnik is a heavy cavalryman, distinguished by a higher cost in metal, but a correspondingly lower cost in wealth. This means that as long as Slavic nations can find sources of metal, such as pelts, or mountains, you can be assured of a large number of heavy cavalry, without exhausting your supply of wealth. That wealth can then be used to purchase mercenaries, such as Kipchak Horse Archers, or Caucasus Mountain Men to bolster your ranks.