Diplomacy is a very important matter. Handled well, it can bring plenty of alien allies together, making your empire incredibly safe and leaving you free to develop in peace.
Once we have detected alien ships, sent an envoy to complete the first contact process, and successfully established contact with an empire, we can find that empire's Homeworld System on the galaxy map. Clicking the flag icon over it opens the diplomacy screen.
Of course, you can also find communications in the UI on the left, then open that nation's diplomacy screen.
On the diplomacy screen, you can see a wealth of information about that nation, including its appearance, name, ethics, origin, population, and planets. However, when communications first open, everything is marked with question marks, and you need more intel.
In the lower-left section, you can see that nation's attitude toward you-from terrible relations to excellent relations-as well as its diplomatic stance, such as Cooperative, Supremacist, or Cosmic Purifier.
Below that, of course, are its relative fleet, economic, and technological strengths: Pathetic, Inferior, Equivalent, Superior, and Overwhelming.
On the right, you can see that nation's relations with other nations: what treaties it has signed and its attitudes toward them.
On the far right is our action menu, with a long list of options to choose from. I'll explain them in detail.
Improve relations: send an envoy to improve relations with that nation. Once relations rise, you can maintain peace and sign certain treaties.
Establish a spy network: send an envoy to establish a spy network in that nation. You can carry out operations such as gathering information, sparking diplomatic incidents, preparing sleeper agents, recruiting assets, extorting favors, smear campaigns, stealing technology, sabotaging Stellar Base facilities, and arming privateers.
Honestly, these operations are mostly damn useless. They just look impressive. Actually