Long before humans existed, advanced aliens species, took to the stars.  Some alien races were just and kind.  Others were cruel and unjust.  Eventually, these two groups met.  This encounter started a rivalry lasting eons.  As the rival groups  advanced, confict between them spread beyond the Milky Way Galalxy.  Whe humanity comes of age.  Intergalactic aggressors  set their sites on habitable planets in the Milky Way Galaxy.  A select few on Earth and nearby solar systems must form alliances to save their people from certain doom.  Only together can the less advanced species survive.  In the age of interstellar travel, humans and similar alien races may watch their worlds go to ruin or save them.