Lots of native american tribes committed genocide and destroyed other tribes. If Tribe A made some artifacts, and then was genocided out of existence by Tribe B, which was then conquered by the Tribe C (USA). Would you want Tribe B to have ownership of the artifacts of tribe B?
Including your 'tribe C' (the USA) with two indigenous tribes (A & B) in your example is highly disingenuous. And self-serving to your contrived hypothetical.