How about making monster the privateers of elemental? I alway's liked the idea of having units that look "neutral" to the enemies. This way you could raid allies while keeping the blame of yourself.

*insert soldier voice* 'Sir, why do we use the beast?'
*insert general voice* 'Because the enemy will see them like beast also, private.'
                               'They can prevent Tarth from getting too strongh by raiding them, and nobody gets the blaim.' 

What also could be cool to see is that monster lairs group together, like they do in Earth here. Then you can have Wildling lands or Drake lands, or the like. This way you can identify different regions by monster type.

*insert peasant voice* 'Don't go to that forest, it's wolf country there!'
*insert arrogant noble voice* 'Ha! I will reclaim that forest for the humans again, have no fear peasantry! Lord Relias is here!'