Turns out I should have been wary of the Jellution Collective.
It's turn 133 now, the Linkin Empire comprises more than 20 worlds, about half of which are fairly well developed. I still have not build any military units, depending on diplomacy to maintain treaties with the Walden Forest and the Jellution Collective.
Unfortunately, my treaty with the latter lapsed, and they attacked one of my colonies. All I had in defense were a couple of militia units, which were quickly dispatched.
I have bought another treaty period of 10 years by paying tribute, but now realize it's time to start devoting attention to the military.
The Linkin Empire is brown, the Walden Forest is lighter brown, in the map below.
