Supply game mode

You should add a game mode where you actually have to get supplys by having supply lines which your enemys can block.
like the Art of War from Sun Tzu.

Actually
The art of wall block is alike breaking enemy's supply line that he cannot supply the walled up city
you can make use of transport to send troops to build a long def wall to isolate the enemy frontier with his major cities
Moreover, you can try to attack and turnblock those transport of enemy to destroy enemy supply force easily

But it seems you add an additional factor to the game
That may need a great change in the game and be a burden to programmer
I am negative to that

I guess it would be cool for a game mode