Complex sentence: Kovacs is on the run after his numerous bloody attacks against an extremist religious order ("Beards"), upon which he has declared a personal vendetta with the express intent of killing every single member, for reasons which are revealed much later in the story.
Split into simpler sentences: Kovacs is on the run after making numerous bloody attacks against an extremist religious order ("Beards"). He has declared a personal vendetta on the Beards with the express intent of killing every single member, for reasons which are revealed much later in the story.