An alliance changes everything: intelligence (you see every member's movements), defence (your allies can send troops to protect you) and rankings.
Without an alliance
The Alliance page offers three things: the list of alliances (name, tag, members, score), create a new alliance (a name of 3 to 60 characters, a tag of 2 to 8) or join an existing one. In that case you are pending: the alliance administrator must accept — or refuse — your application. You can cancel your request.
Member
You see the alliance's description, its members and their scores. Mail sent to “*” reaches the whole alliance. You can leave whenever you want.
Administrator
If you created the alliance, you administer it: you edit the description, expel a member, and handle requests — the number in brackets tells how many players await your answer.
The tag appears in square brackets next to your name everywhere in the game: [CORE], [THSK]…