We already have the weapons with the potential to kill us all.
Or we can do it in stages, with heat and chemical pollution.
As Stalin once said, quantity is its own quality. The perfectly cut chamber is either a matter of having one totally gifted artisan with decades of work, or 50,000 workers to ensure each piece fitted perfectly.
My own theory about the absence of aliens is - any alien with common sense would keep well away.
A century ago, a machine that could scan one's body from head to toe, and pinpoint every internal defect, would be dismissed as science fiction. CT and PET scanners would be called miracles by anyone in the Middle Ages.