Upon being freed from the bag, the humans killed the wolf, thus bringing death into the world.
They knew the humans could and would kill them all, with their machines.
If, that was, the humans killed them fast enough.
"Logically humans may kill themselves off, pushing a similar pedal."
This surprise attack caused much damage to the planets where the humans lived and killed most of their populations.
The primitive humans killed some of the elves and drove the rest away.
But that was before humans had killed the first starfaring alien they'd ever met.
There it was in so many words: humans had killed Cynthians.
Since at least the 17th century some humans have killed certain wildlife species in locations not under their land ownership.
The few survivors reported that the old humans had killed the settlers because of what they were.