While Human Unity uses weapons which would enthral the 21st Century warlord, from shipboard weapons to intelligent bullets, the greatest and most terrible weapon is the Master Expert, artificial intelligences designed for war. But this weapon does not inspire fear in the average person. It is just a brain, a ruthless brain designed to win wars whatever the cost, but still only a brain.
The Earth provided us with a catalogue of terrors from which to build an army of Terror Weapons. Like the Digger Wasp which paralyses it’s insect prey and implants eggs into the still-living creature. Or the Phorid fly which attacks red ants, injecting them with larvae which migrate to the ant’s head and consume, using the head as a pupal case. What we do know is that the Conquest society have built upon their memories of Earth – built from the genebanks they brought with them.
We don’t need to imagine that other races on other planets across the wormhole network have their own horrors to build upon. The Trader archives contain several examples of bio-engineered guerilla weapons which decimated entire worlds, complete with dire warnings to stay away. These weapons are recorded as causing extinction events on the home planets where they originated.