My Suggestions
Instead of just one type of alliance, the one leader, five vice and everyone else is a member system, there should be different government types you can choose from.
Examples: Dictatorship: One leader, all else members. Monarchy: One leader five vices. Republic: Three Leaders, possibly group of vices to be senate. Democracy, Lassez-faire and so on.
Cities:
You should be able to name your main city, and rename and/or resign branch cities.
Foriegn Relations:
There should be a section in the alliance where you can designate allied alliances and alliances you are at war with.
Aid: You should be able to send your friends resources, money and possibly reinforce their cities with your troops.
That's all for now, thanks for reading you guys made a great game.
ROME