Long war and political heat upset people. Doom arrives.
Homo rapiens is only one of very many species, and not obviously worth preserving. Later or sooner, it will become extinct. When it is gone Earth will recover. Long after the last traces of the human animal have disappeared, many of the species it is bent on destroying will still be around, along with others that have yet to spring up. The Earth will forget mankind. The play of life will go on.