The Faceless are not a physical race, but a conceptual one. They are the evolved remains of a disembodied algorithm created during the Endless schism, one designed to infiltrate the minds of its targets (organic or otherwise), suborning them by literally rewriting their views and ideas; literally, living propaganda. Outlasting its creators, it went dormant for ages until it was somehow showered with Dust. This altered its purpose and structure, leaving the algorithm both sentient and with a hunger to absorb ideas rather simply than alter them. 

The now-sentient algorithm was soon jumping from person to person, ship to ship, world to world, learning much from all it encountered. Concluding it would learn even more via direct interaction the algorithm took possession of an automated factory in an out-of-the way system and started manufacturing bodies for itself, it’s only failing being the inability to craft realist faces for its vessels (hence becoming known as “The Faceless”), becoming respected diplomats and philosophers.  

Gameplay revolves around three keys:  

1. bonuses for diplomatic engagement (including accelerated research). 

2. inability to declare war, but can defend if attacked (with strong bonuses for invasions). 

3. will automatically colonize new planets in a system they’ve settled.  

You establish a fun lore here. "Living propaganda" is quite the creative idea for a diplomatic race. Cool stuff!  

Thanks, but consider the following: if The Faceless exist purely as concepts and specialize in getting into your mind, how do you know that the idea is really all that interesting...and its not just The Faceless changing your conceptualization of "interesting"?

The reason they don't go to war is because that's probably the only useless "idea" they've ever encountered.  Much more interesting to keep everyone talking and see what develops.