I think you are asking for an impossibility. There never was and never will be a general, who would kill in the name of War. Killing is conducted on very different premise.
- Political control over trade routes or neighboring territories
- A struggle over political influence in the country or territory
- Dynastical quarrels over some territory
- Raids to another territory with the purpose of pillage
- Killing as a demonstration of power as in punishing those disobedient
- Religious intolerance
- Ideological intolerance
- Defending your own county from invaders
- Stupid reasons (loss in a soccer game)
Most of the generals as well as other people think that they represent good and their enemies are evil. Even the most horrible people in history like Genghis Khan, Tamerlane, Ivan the Terrible, Henry IX (the guy who concocted the Saint Bartholomew’s Day Massacre) did this because of very practical considerations. Even Richard the Lionheart, who enjoyed the murder like a serial killer, didn’t want to destroy the entire species (only to subjugate them)
Only a completely insane person could be thinking about destroying an entire species. However, I doubt such a person would be able to obtain the position of a general in any army in the World.
There are a lot of expedients that may make such a scenario plausible. Especially in the realm of science fiction.
I suggest you sit back relax and see what the authors come up with.
When the question makes no sense the answers will be just as nonsensical. LOL