As also announced on Discord by our Community Manager MadameLeota today, here is an explanation of the new rule added with the latest update (version 9.5.0):

- If an Overlord is offline for 14 days, all members get a message.
- After 7 days, the ownership is transferred to the member with the highest rank.
- If there are 2+ players with the same high rank, then it should go to the player who logged first after the 7-days message.
- If there are 2+ who logged at the same time, then it goes to the one who joined the alliance first.

If you have not yet joined the official Discord server, here is the invitation:
https://discordapp.com/invite/dragonsofatlantis