Because the Jedi and Sith organizations do not by any means have a monopoly on the Force, or the light and dark sides. There are numerous Force religions and philosophies in the Star Wars galaxy of both light and dark standing.
It is very plausible that this other group of dark side users may have had dreams of galactic conquest. One does not need be associated with fallen Jedi in order to have this goal in mind. Just look at the Yuuzhan Vong, for example.
Originally Posted by a silly noob
YOURS VERY SLOW ! PLS NEW PROGRESSS PLS NEW UPDATES PLS DARK FORCES FİNAL VERSİON
İ CAN WAİTİNG KOTF PART 1 RELEASED 5 YEAR AND İTS 1 MAN ( OSMAN GUNYAZ DEVELOPERS ) BUT YOURS VERY PEOPLE İ CANT WAİTİNG 5 YEARS