It is a good idea, However if one alliance becomes too strong, or opens up and lets everyone in then the game will be completely overrun by one group and the others would not stand a chance.
Unless you limit the number of players in an alliance it could work

I think it would be a good idea to set up "Trade Routes" It would be nice if there was a bigger emphasis on trading within the game maybe a section at 1N 1W where players could directly complete trades instead of having to go through the forums?
Also with the "Trade Routes" idea, you could blockade trade routes to earn some MD if you introduce a new "Skill" that you could upgrade which gives you more MD for blockading trade routes. That would be a unique feature in having an upgraded "Skill" rather than an upgraded "Item"