Quite possible that the event, as well as the in-game banner promoting the alliance feature of the game might have been drivers behind this.
In any case, it's good that you've got recruits!
It'll help to capitalize on it, by attempting to communicate with them, and get some alliance chatter going on over in-game chat.
It might also be a good time to start an alliance war, to try and get the new allies hooked to the alliance.
It's probably going to take some work, but, the rewards will be worth it!
Wishing you the best with your initiatives and with building up the alliance!
We'll all be happy to help you with suggestions to help you build up the alliance!
Cheers and good luck!