They attempt to make their neighbors their subjects. The Fallen Empire awakens because one of the other Empires in the galaxy has become too powerful (collected 70k or more in Fleet Power combined, or has conquered a Fallen Empire planet).

If the Endgame Crisis occurs and has not been dealt with within five years, there's a chance that Fallen Empires will awaken and attempt to rally the galaxy against the Crisis by forming a large Federation. If you complete a Task, accept a Request, or have a Patronizing relationship with the Fallen Empire, they may send you a Gift.

Allow inoculations (allow code changes if you are a machine empire).

Abandon systems you own that have hyperlanes into their territory.

Send them one of your Scientist Leaders who is above level five.

Abandon planets that you have colonized that the Fallen Empire considers to be Holy Worlds.

Go to war against another Empire to force them to outlaw AI.

Go to war against another Empire and force them to outlaw purging.

Send them the acquired brain scans from the 'Limbo' special project.

Send a Population to one of their worlds (The Preserve).

If you refuse their Demand, they may go to war against you, and the war goal will be exactly the same as the Demand. If you give into their Demand, the Fallen Empire's opinion of you increases by 25. You will only receive a Demand if the Fallen Empire has an Opinion of you below -100 (otherwise, they let it slide).

Demands are exactly what they sound like you've done something that the Fallen Empire doesn't like, and they want you to undo it.

If you accept the task but don't complete it, their Opinion of you will fall more than that. Declining the task will make their Opinion of you fall by 25. If you complete the task, the Fallen Empire's Opinion of you goes up by 100.

Tasks usually ask you to fight another Empire in the galaxy (always one of your Rivals).

If accepted, they will increase the Fallen Empire's Opinion of you by 100 if accepted, or decrease it by 50 if declined.

Requests usually ask you for a favor in exchange for a better relationship with this Fallen Empire.

Other than those, there are three main types of unique interactions you may have with a Fallen Empire, which will be prompted by the Fallen Empire contacting you.

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