The main antagonists are the members of the Morthan Solidarity, originally a group of genetically improved humans.
A full-blown war erupts in the course of "Voyage of the Star Wolf", as the Morthan Solidarity starts an offensive against the Terran Alliance.
Gerrold had planned to develop this concept into a TV series, as he writes in an introduction to Voyage of the Star Wolf.
Gerrold referred to the concept as "World War II in space," and intended it as a stylistic opposite of Star Trek (particularly its Next Generation incarnation) by setting the main characters on a small, dingy spacecraft that had little respect in the fleet rather than on the flagship.
The central story, without the frame, eventually became Gerrold's Star Trek novel The Galactic Whirlpool.