How do you actually join an alliance?

Do you have to be invited first? I can't find any options on the mission.

Do you have to be invited first? I can't find any options on the mission.

You can pm someone already in an alliance and ask to join (you can tell if they are in one by clicking on their dwelling and/or the hero name (right click on that to open the hero page if you want more information). 

You can start your own alliance with a level 5 Mission. There is an option in the mission for starting your own alliance when the mission is high enough.

Or, you get invited into an already established alliance.

Thank you for your information, I will try to find someone in an alliance now.

It took me a while to search the forum to find how friend someone. Here's a short version of what worked for me. 

How to add a neighbor as a Friend: Click on their main dwelling, choose the ? icon, then right click on their name, then use button on right to add as friend.