Complex sentence: It was influential in providing the mythology and ideology inherent in the rebirth of the Ku Klux Klan (KKK), after being filtered through a retelling in the 1915 silent movie "The Birth of a Nation".
Split into simpler sentences: It was influential in providing the mythology and ideology that helped support the revival of the Ku Klux Klan (KKK). The novel received most exposure as the basis of the 1915 silent movie "The Birth of a Nation".