Complex sentence: The story is set in the near future, when Earth is threatened by a spaceborne virus that turns humans into violent creatures, and enhanced soldiers are fighting a war against them in order to ensure the survival of the human race.
Split into simpler sentences: The story is set in the near future, when Earth is threatened by a "spaceborne virus" that turns humans into violent creatures. "Enhanced soldiers" are fighting a war against the violent creatures in order to ensure the survival of the human race.