If we're adding detail to the story because we think the reader might not be aware of why there weren't many bison left, I'm not sure: > Bison had become nearl

If we're adding detail to the story because we think the reader might not be aware of why there weren't many bison left, I'm not sure: > Bison had become nearly extinct due to genocide by European settlers is going to help. Any reader who'd benefit from specifying why bison had been largely wiped out, probably won't connect the dots here, and will instead read that as genocide against bison. Readers who read "genocide" as referring to "genocide against indigenous people, part of which was eradication of bison" didn't need any of this called out to begin with.