In the game you can put all the troops in one country and then conquer with the same troops as many countries as you want or until the troops are exhausted. So is my idea that there is a game option and if you activate it each unit can only attack one country (But not only one time, the unit can attack the same country as often as you would, but after that the same unit can't attack a other country.) So you can't longer put all your troops in one country and then conquer with them a whole continent, with this feature you have to think more about the troop placement and which country you attack. This would make risk a more strategic and less luck game.
Kjell