Diplomacy is what happens when you have more than two (human) players in a war-game of any sort. Pretty soon, they start talking to each other, making alliances, etc. Stars! is no exception, and actually includes features designed specifically for the diplomatic part of the game (such as the friend/neutral/enemy status options, and in-game messaging).
There are a number of articles in the Article Library about diplomacy.
Pages in category "Diplomacy"
The following 3 pages are in this category, out of 3 total.