Morning Discussion

Sci-Fi short story help
Trying to remember the title of a short story I read a long time ago. The plot was something like this:

A pilot/group? of humans is on a deep space mission, looking for hospitable planets, but have so far been unable to find any nearby planets to Earth in tens of light years( I think. this detail is kind of important )
They eventually come upon a planet? and there are some aliens? or some kind of encounter, and they are told the following story:
There was once a civilization that was prosperous, and expanded to control a bunch of stars/planets, but there was a war of some kind with other civilizations, and one of the civilizations developed a weapon that blew up planets/stars. They used this weapon to basically seal in the originally belligerent species, as well as killing off all life/planets surrounding its home system, effectively penning them off from the rest of the galaxy.
The person/being telling this story mentions some detail about this empire cutting off an arm or hand? of its people/criminals? (I don't recall which.) The man being told the story, upon hearing this detail, recalls Earth's history of a civilization, (I think it was implied the Romans?) used to use this method of punishment, and begins to wonder if perhaps there was some connection with Earth not finding any hospitable planets and this story he is hearing.... at which point the being/alien telling him one of the consequences of that civilization being defeated is they don't get to expand, and the entire story ends with the implication that the aliens will kill the humans. (The big reveal at the end is that humans were once a vast galactic power, but got bombed to the stone age and had to start over, but are stuck in a holding pen/prison)

The story reminds me of The Crystal Spheres, by David Brin, but the details are different. Anyone got a clue who wrote this or the title? I'm thinking Clarke or Asimov, but going through their short stories hasn't turned up anything yet.