Genocide names the international crime of deliberately killing of large group of people based on their group identity.
In David Mack's Star Trek: Titan novel Fortune of War, the pure energy being exterminates the Husnock, a 50 billion strong aggressive species bent on conquering the universe.
In Men Against Fire Men Against Fire episode of Black Mirror, Season 3, a near future human society uses sophisticated mind control implants to force its soldiers to hunt down and massacre innocent human mutants.