Well, the vassalage does not work as they intend. It does by no means drain the economy. I was playing with a friend of mine. He attacked his neighbour and forced them to become vassals. He then continued to attack another one, and with his vassal conquered it fast, making that one also a vassal. He copied this with 6-7 other nations, always getting more vassals to attack together with. None of the vassals were strong enough to dare a war against him. Doing this he became an unstoppable force. His economy was great because he could trade with his vassals as described earlier in this topic... So, I believe this is kind of an exploit. Sorry for bad spelling and english Was in a hurry!