Should You Complete the Subterranean Civilization in Stellaris?

Although it’s a 4X strategy game, Stellaris offers numerous narrative events that enhance its appeal and depth, making it popular for almost ten years. One frequently encountered plotline is the Subterranean Civilization event, where a newly-colonized planet is home to a sentient, industrial society living underground.

There isn’t a single “correct” way to handle this event in gameplay, but you may prefer guiding it to a specific outcome. This guide will explain how your choices affect the resolution of the Subterranean Civilization storyline.

How to Start the Subterranean Civilization Event

As with many events in Stellaris, the Subterranean Civilization happens at random. There’s a slight chance it will trigger when you settle on a new planet, but once it occurs, it won’t repeat for the game’s duration.

The storyline will kick off within a few years of your colony’s establishment if a planet hosts a Subterranean Civilization. The timing is randomized, but if you go five years without seeing the event, you can assume it won’t occur on that planet.

Should You Establish Communications or Destroy the Subterranean Civilization?

Upon discovering the Subterranean Civilization, you’ll have the option of two Special Projects: Establish Communications or Pre-Emptive Strike. Communicating allows you to attempt a coexistence, but poor relations may still lead to conflict. Opting for the Pre-Emptive Strike means permanently eliminating the Subterranean Civilization, negating any chance of reconciliation.

Pre-Emptive Strike

Choosing to eliminate the Subterranean Civilization will result in your military automatically executing a coordinated strike when the Special Project concludes; there’s no need for troop deployment or orbital attacks. The planet will have blockers added that, once cleared, will enable Agricultural, Mining, and Generator Districts as your colony repurposes the old tunnels.

About 20 years after their destruction, you will receive a follow-up event. Typically, this will offer minor bonuses like Energy Credits, but you may occasionally get additional Urban District space. However, be mindful—a small chance exists for an earthquake to strike, resulting in Devastation for your colony.

Once this second event occurs, the Subterranean Civilization narrative concludes, and you’ll see no further events related to it.

Establish Communications

By establishing communications, you gain a small boost to Society Research as long as your relations remain positive. However, the Subterranean Civilization may regularly request favors from you. Their mining activities could also lead to earthquakes that inflict damage on your colony.

Neglecting their requests or demanding apologies for damages will harm relations, while fulfilling their demands and overlooking their errors can boost goodwill. If you maintain a balance, not worsening relations more often than you improve them, they may occasionally gift you Minerals.

If the negative interactions exceed your positive ones by three times, they will become hostile. You’ll receive a warning about a month before the attack. While their forces are weaker than your advanced troops, they can overwhelm a colony lacking Strongholds or additional armies.

• If you defeat them, you’ll unlock a Special Project to destroy the Subterranean Civilization. This is similar to the Pre-Emptive Strike but won’t trigger a follow-up event.
• If they take control of the planet, they become a spacefaring empire and gain control of the entire system.